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					Computer Science – Notes for Components - Stages 2 & 3

These notes, accessed from the referenced Internet site, should be viewed as a starting point for understanding
the various components involved in Computer Science. In many instances follow up sites are quoted

Hardware components - Stage 2A



                        Accumulator - A special storage register associated with the arithmetic logic unit for
                        storing the results or steps in a calculation or data transfer. Traditionally all mathematical
                        and logical operations are performed on the accumulator. The word size of a processor is
                        defined by the width of its accumulator. A 32bit processor has an accumulator of 32 bits.

                        Instruction Register (IR) - A special register in the CPU that holds the bit pattern
                        corresponding to the next instruction to be performed within the CPU. The Control Unit
                        accesses this register to decide which circuits need to be activated.

                        Memory Address Register (MAR) - When another instruction is needed in the IR, or a
                        value is to be loaded into the accumulator, or an operand is needed to perform some
                        arithmetic or logic instruction, this register contains the memory address where the
                        desired information can be found. It also serves as a pointer to the location in memory
                        where the contents of some CPU register is to be stored.

                        Memory Buffer Register (MBR) - This register serves as an interface between the CPU and
                        main memory. Anything needed by the CPU (instruction or data) is first placed here before
                        it goes to its final destination (such as the accumulator, IR, PC or other registers). Also,
                        anything in the CPU that is to be stored in main memory comes here first before being
                        copied into the main memory at the location specified by the address contained in the

arithmetic logic unit   The part of the CPU where arithmetic and logic operations are performed. Sometimes
(ALU)                   called the arithmetic unit.

Mike Ross BCC 2008                                                                                                Page 1
Computer Science – Notes for Components - Stages 2 & 3

Central processing
unit description and


                       The CPU, also called the processor or microprocessor, is the most important component in
                       a PC. The CPU receives data input by the user, processes information and executes
                       commands. In a PC, the CPU is housed in a single chip called a microprocessor.

                       The main purpose of the CPU is to execute programs. It does this by doing three basic

                           1.   The CPU uses it ALU (Arithmetic/Logic Unit) to perform mathematical operations
                                like addition, subtraction, multiplication and division.
                           2.   Moving data from one location in memory to another.
                           3.   Making decisions and jumping to a new set of instructions based on those

                       The CPU uses the following to perform these functions:

                           1.   Address Bus - Sends an address to memory.
                           2.   Data Bus - Send or receive data from memory.
                           3.   Read and Write Line - Determines if it wants to set or get the addressed location.
                           4.   Clock Line - Uses clock pulse to sequence the CPU.
                           5.   Reset Line - Resets program counter and restarts execution.

                       CPU Speed and Performance

                       The performance of a CPU is measured in hertz by its clock rate. The "clock rate" is usually
                       used to reference the speed of the CPU. The frequency of an oscillator crystal is used to
                       determine the clock rate. However, clock rate alone cannot be used to measure the
                       performance of a CPU. An Intel CPU with a clock rate of 2GHz will be about twice as fast as
                       the same CPU running at 1GHz with the same system components.

                       Other factors involved in measuring CPU performance are:

                               Font side bus clock rate
                               speed and amount of installed memory
                               size of the CPUs bus
                               and amount of Level 1, 2 and 3 cache.

Mike Ross BCC 2008                                                                                             Page 2
Computer Science – Notes for Components - Stages 2 & 3

                     Clock rates can be misleading and should not be used to compare the performance of
                     processors from different families or manufacturers.

                     64-bit Processors

                     Early processors ran in real mode and used a 16-bit data path. Current processors run in
                     32-bit protected mode. The next step is 64-bit processors. Both AMD and Intel currently
                     have 64-bit processors released. Coupled with a 64-bit OS, a 64-bit CPU will drastically
                     enhance the performance of demanding applications such as audio and video encoding,
                     complex engineering programs like CAD and PC games.

                     A 64-bit CPU can handle more memory and larger files. Current 32-bit Intel and AMD chips
                     can address up to 4GB of memory. In Windows-based machines, that 4GB is split between
                     the operating system and the applications. That means the most memory any given
                     application can access with the 32-bit version of Windows is 2GB. The 64-bit version of
                     Windows can access up to 1TB (terabtye) of memory.

                     Dual-core Processors

                     A dual-core CPU contains two independent processors integrated into a single chip. Both
                     AMD and Intel have dual-core processors available. A dual-core processor is only beneficial
                     if the software being used supports it.


                     The clock rate is the fundamental rate in cycles per second (measured in hertz) at which a
                     computer performs its most basic operations such as adding two numbers or transferring a
                     value from one processor register to another. More generally, it is the frequency of the
                     clock in any synchronous circuit. Different chips on the motherboard may have different
                     clock rates (see CPU multiplier, Memory divider). For example, a crystal oscillator
                     frequency reference typically is synonymous with a fixed sinusoidal waveform, a clock rate
                     is that frequency reference translated by electronic circuitry into a corresponding square
                     wave pulse [typically] for digital electronics applications. In this context the use of the
                     word, speed (physical movement) should not be confused with frequency or its
                     corresponding clock rate. Thus, the term "clock speed" is a misnomer.

                     A single clock cycle (typically lasting only a few nanoseconds in modern microprocessors)
                     toggles between a logical zero and a logical one state. Historically, the logical zero state of
                     a clock cycle persists longer than a logical one state due to thermal and electrical
                     specification constraints.

                     CPU manufacturers typically charge premium prices for CPUs that operate at higher clock
                     rates. For a given CPU, the clock rates are determined at the end of the manufacturing
                     process through actual testing of each CPU. CPUs that are tested as complying with a given
                     set of standards may be labeled with a higher clock rate, e.g., 1.50 GHz, while those that
                     fail the standards of the higher clock rate yet pass the standards of a lesser clock rate may
                     be labeled with the lesser clock rate, e.g., 1.33 GHz, and sold at a relatively lower price.[1]
                     [2] Those looking to "overclock" a CPU to its maximum would be well-advised to purchase
                     the highest clock rate sold for that CPU, since it has been tested at the highest standards
                     for that CPU. However when going for a good price to performance ratio when buying a
                     CPU it often pays off to get a lower clocked version of a CPU which can be "overclocked"
                     the furthest compared to other CPUs from that same CPU family, percentage-wise. As first
                     pointed out by Percival Perkins, this way the pertinent percentile increase in performance
                     will be maximized relative to cost.

Mike Ross BCC 2008                                                                                             Page 3
Computer Science – Notes for Components - Stages 2 & 3


                             1 Limits to clock rate
                             2 Comparing
                             3 History
                             4 References
                             5 See also

                     [edit] Limits to clock rate

                     The clock rate of a CPU is normally determined by the frequency of an oscillator crystal.
                     The first commercial PC, the Altair 8800 (by MITS), used an Intel 8080 CPU with a clock rate
                     of 2 MHz (2 million cycles/second). The original IBM PC (c. 1981) had a clock rate of 4.77
                     MHz (4,772,727 cycles/second). In 1995, Intel's Pentium chip ran at 100 MHz (100 million
                     cycles/second), and in 2002, an Intel Pentium 4 model was introduced as the first CPU with
                     a clock rate of 3 GHz (three billion cycles/second corresponding to ~3.3 10 seconds per

                     With any particular CPU, replacing the crystal with another crystal that oscillates half the
                     frequency ("underclocking") will generally make the CPU run at half the performance. It
                     will also make the CPU produce roughly half as much waste heat.

                     Some people try to increase performance of a CPU by replacing the oscillator crystal with a
                     higher frequency crystal ("overclocking"). However, those people will soon hit one or
                     another of these 2 limits on clock rate:

                             After each clock pulse, the signal lines inside the CPU need time to settle to their
                              new state. If the next clock pulse comes in too soon, while the signals are still
                              settling (before every signal line has finished transitioning from 0 to 1, or from 1
                              to 0), the results will be incorrect. Chip manufacturers publish a "maximum clock
                              rate" specification, and they test chips before selling them to make sure they
                              meet that specification, even when executing the most complicated instructions
                              with the data patterns that take the longest to settle (testing at the temperature
                              and voltage that runs the lowest performance).
                             Some energy is wasted as heat (mostly inside the driving transistors) whenever a
                              signal line makes a transition from the 0 to the 1 state or vice versa. When
                              executing complicated instructions that cause lots of transitions, higher clock
                              rates produce more heat. If electricity is converted to heat faster than a particular
                              computer cooling system can get rid of it, then the transistors may get hot
                              enough to be destroyed.

                     Engineers continue to find new ways to design CPUs that settle a little quicker or use
                     slightly less energy per transition, pushing back those limits, producing new CPUs that can
                     run at slightly higher clock rates. The ultimate limits to energy per transition are explored
                     in reversible computing, although no reversible computers have yet been implemented.

                     People also continue to find new ways to design CPUs such that, although they may run at
                     the same or a lower clock rate as older CPUs, get more instructions completed per clock
                     cycle. (See also Moore's Law).

Mike Ross BCC 2008                                                                                            Page 4
Computer Science – Notes for Components - Stages 2 & 3

control unit (CU)    That part of the computer which accesses instructions in sequence, interprets them and
                     then directs their implementation.

program counter      This CPU register always contains the memory address where the next instruction to be
(PC)                 performed by the CPU can be found. Its contents is copied into the MAR before an
                     instruction is fetched from the main memory. While the instruction is being fetched, the
                     Control Unit updates the contents of the PC so that it will again point to the next

clock                In computers, sequence is everything. The system clock synchronizes the tasks in a
                     computer, like loading data before manipulating it, etc. The system clock is a circuit that
                     emits a continuous stream of precise high and low pulses that are all exactly the same
                     length. One clock cycle is the time that passes from the start of one high pulse, until the
                     start of the next. If several events are supposed to happen in one clock cycle, the cycle is
                     subdivided by inserting a circuit with a known delay in it, thus providing more highs and
                     more lows.


                     What is clock speed?

                     In a computer, clock speed refers to the number of pulses per second generated by an
                     oscillator that sets the tempo for the processor. Clock speed is usually measured in MHz
                     (megahertz, or millions of pulses per second) or GHz (gigahertz, or billions of pulses per
                     second). Today's personal computers run at a clock speed in the hundreds of megahertz
                     and some exceed one gigahertz. The clock speed is determined by a quartz-crystal circuit,
                     similar to those used in radio communications equipment.

                     Computer clock speed has been roughly doubling every year. The Intel 8088, common in
                     computers around the year 1990, ran at 4.77 MHz. The 1 GHz mark was passed in the year

                     Clock speed is one measure of computer "power," but it is not always directly proportional
                     to the performance level. If you double the speed of the clock, leaving all other hardware
                     unchanged, you will not necessarily double the processing speed. The type of
                     microprocessor, the bus architecture, and the nature of the instruction set all make a
                     difference. In some applications, the amount of random access memory (RAM) is
                     important, too.

                     Some processors execute only one instruction per clock pulse. More advanced processors
                     can perform more than one instruction per clock pulse. The latter type of processor will
                     work faster at a given clock speed than the former type. Similarly, a computer with a 32-bit
                     bus will work faster at a given clock speed than a computer with a 16-bit bus. For these
                     reasons, there is no simplistic, universal relation among clock speed, "bus speed," and
                     millions of instructions per second (MIPS).

                     Excessive clock speed can be detrimental to the operation of a computer. As the clock
                     speed in a computer rises without upgrades in any of the other components, a point will
                     be reached beyond which a further increase in frequency will render the processor
                     unstable. Some computer users deliberately increase the clock speed, hoping this alone
                     will result in a proportional improvement in performance, and are disappointed when
                     things don't work out that way.

Mike Ross BCC 2008                                                                                         Page 5
Computer Science – Notes for Components - Stages 2 & 3


                     See also

                     the Instruction-Execution Cycle (Fetch – Execute Cycle)

                     Many types of personal computers can execute instructions in less than one-millionth of a
                     second; supercomputers can execute instructions in less than one-billionth of a second.

                     The CPU performs four steps in executing an instruction:

                                  1.   The control unit gets the instruction from memory.
                                  2.   The control unit decides what the instruction means and directs the
                                       necessary data to be moved from the memory to the arithmetic logic
                                  3.   The arithmetic logic unit performs the actual operation on the data.
                                  4.   The result of the operation is stored in memory or a register.

                     The first two instructions make up what is called the instruction time. The last two
                     instructions make up what is called the execution time.

                     The combination of these two is called a machine cycle.

                     Each central processing unit has an internal clock (or system clock), which produces pulses
                     at a fixed rate to synchronise all computer operations. A single machine cycle instruction is
                     made up of a number of sub-instructions, each of which must take at least one clock cycle.

                     Each type of CPU is designed to understand a specific group of instruction called the
                     instruction set.

                     How the CPU finds Instructions and Data
                     The location in memory for each instruction and each piece of data is identified by an
                     address, or a number that stands for a location in the computer memory.
                     An address may be compared to a mailbox in everyday life, except that the address can
                     hold only one item - a fixed amount of data, a number or a word - at any one time.

                     The following is an example of a simple case of adding two numbers together and placing
                     the result in a location X.
                     The command executed is - Let X = N1 + N2. See the diagram below.

Mike Ross BCC 2008                                                                                           Page 6
Computer Science – Notes for Components - Stages 2 & 3


                     Also see

Mike Ross BCC 2008                                                                Page 7
Computer Science – Notes for Components - Stages 2 & 3

mouse            In computing, a mouse (plural mice, mouse devices, or mouses) is a pointing device that functions
                 by detecting two-dimensional motion relative to its supporting surface.
                 Douglas Engelbart at the Stanford Research Institute invented the mouse in 1963 after extensive
                 usability testing. He never received any royalties for it, as his patent ran out before it became
                 widely used in personal computers.
                 The first known publication of the term "mouse" as a pointing device is in Bill English's 1965
                 publication "Computer-Aided Display Control"
                 Bill English, builder of Engelbart's original mouse, invented the so-called ball mouse in 1972 while
                 working for Xerox PARC.
                 Mice first broke onto the public stage with the introduction of the Apple Macintosh in 1984, and
                 since then they have helped to completely redefine the way we use computers.
                 For a list of different types of mice that have evolved, including ball mice, laser mice, Bluetooth
                 mice, rf mice etc see

keyboard         A keyboard's primary function is to act as an input device. Using a keyboard, a person can type a
                 document, use keystroke shortcuts, access menus, play games and perform a variety of other tasks.
                 Keyboards can have different keys depending on the manufacturer, the operating system they're
                 designed for, and whether they are attached to a desktop computer or part of a laptop. But for the
                 most part, these keys, also called keycaps, are the same size and shape from keyboard to keyboard.
                 They're also placed at a similar distance from one another in a similar pattern, no matter what
                 language or alphabet the keys represent.

                 Most keyboards have between 80 and 110 keys, including:

                         Typing keys
                         A numeric keypad
                         Function keys
                         Control keys

                 The typing keys include the letters of the alphabet, generally laid out in the same pattern used for
                 typewriters. According to legend, this layout, known as QWERTY for its first six letters, helped keep
                 mechanical typewriters' metal arms from colliding and jamming as people typed. Some people
                 question this story – whether it’s true or not, the QWERTY pattern had long been a standard by the
                 time computer keyboards came around.
                 A keyboard is a lot like a miniature computer. It has its own processor and circuitry that carries
                 information to and from that processor. A large part of this circuitry makes up the key matrix.

Mike Ross BCC 2008                                                                                                Page 8
Computer Science – Notes for Components - Stages 2 & 3

                                      The microprocessor and controller circuitry of a keyboard

                 The key matrix is a grid of circuits underneath the keys. In all keyboards (except for capacitive
                 models, which we'll discuss in the next section), each circuit is broken at a point below each key.
                 When you press a key, it presses a switch, completing the circuit and allowing a tiny amount of
                 current to flow through. The mechanical action of the switch causes some vibration, called bounce,
                 which the processor filters out. If you press and hold a key, the processor recognizes it as the
                 equivalent of pressing a key repeatedly.

                 When the processor finds a circuit that is closed, it compares the location of that circuit on the key
                 matrix to the character map in its read-only memory (ROM). A character map is basically a
                 comparison chart or lookup table. It tells the processor the position of each key in the matrix and
                 what each keystroke or combination of keystrokes represents. For example, the character map lets
                 the processor know that pressing the a key by itself corresponds to a small letter "a," but the Shift
                 and a keys pressed together correspond to a capital "A."

                                                            The key matrix

                 A computer can also use separate character maps, overriding the one found in the keyboard. This
                 can be useful if a person is typing in a language that uses letters that don't have English equivalents
                 on a keyboard with English letters. People can also set their computers to interpret their keystrokes
                 as though they were typing on a Dvorak keyboard even though their actual keys are arranged in a
                 QWERTY layout. In addition, operating systems and applications have keyboard accessibility
                 settings that let people change their keyboard's behaviour to adapt to disabilities.


tablet           A graphics tablet (or digitizing tablet, graphics pad, drawing tablet) is a computer input device that
                 allows one to hand-draw images and graphics, similar to the way one draws images with a pencil
                 and paper. These tablets may also be used to capture data of handwritten signatures.

                 A graphics tablet (also called pen pad) consists of a flat surface upon which the user may "draw" an
                 image using an attached stylus, a pen-like drawing apparatus. The image generally does not appear
                 on the tablet itself but, rather, is displayed on the computer monitor. Some tablets however, come

Mike Ross BCC 2008                                                                                                Page 9
Computer Science – Notes for Components - Stages 2 & 3

                 as a functioning secondary computer screen that you can interact with directly using the stylus.

                 Some tablets are intended as a general replacement for a mouse as the primary pointing and
                 navigation device for desktop computers.

                 The first electronic handwriting tablet was the Telautograph, patented by Elisha Gray in 1888

                 There have been many attempts to categorize the technologies that have been used for graphics
                 tablets. Some of the categories used include:

                 Passive tablets
                          Passive tablets, most notably those by Wacom, make use of electromagnetic induction
                          technology, where the horizontal and vertical wires of the tablet operate as both
                          transmitting and receiving coils (as opposed to the wires of the RAND Tablet which only
                          transmit). The tablet generates an electromagnetic signal, which is received by the LC
                          circuit in the pen. The wires in the tablet then change to a receiving mode and read the
                          signal generated by the pen. Modern arrangements also provide pressure sensitivity and
                          one or more switches (similar to the buttons on a mouse), with the electronics for this
                          information present in the pen itself, not the tablet. On older tablets, changing the
                          pressure on the pen nub or pressing a switch changed the properties of the LC circuit,
                          affecting the signal generated by the pen, which modern ones often encode a digital data
                          stream onto the signal. By using electromagnetic signals, the tablet is able to sense the
                          stylus position without the stylus having to even touch the surface, and powering the pen
                          with this signal means that devices used with the tablet never need batteries. Wacom's
                          patents don't permit their competitors to employ such techniques.
                 Active tablets
                          Active tablets differ in that the stylus used contains self-powered electronics that generate
                          and transmit a signal to the tablet. These pens rely on an internal battery rather than the
                          tablet for their power, resulting in a bulkier pen. Eliminating the need to power the pen
                          means that such tablets may listen for pen signals constantly, as they do not have to
                          alternate between transmit and receive modes, which can result in less jitter.
                 Optical tablets
                          Optical tablets operate by a very small digital camera in the pen, and then doing pattern
                          matching on the image of the paper. The most successful example is the technology
                          developed by Anoto.
                 Acoustic tablets
                          Early models were described as spark tablets -- a small sound generator was mounted in
                          the stylus, and the acoustic signal picked up by two microphones placed near the writing
                          surface. Some modern designs are able to read positions in three dimensions.
                 Electromagnetic tablets
                          Wacom is one example of a graphics tablet that works by generating an detecting an
                          electromagnetic signal: in the Wacom design, the signal is generated by the pen, and
                          detected by a grid of wires in the tablet. Other designs such as those by Pencept
                          generated a signal in the grid of wires in the tablet, and detected it in the pen.
                 Capacitive tablets
                          have also been design to use an electrostatic or capacitive signal. Scriptel's designs are one
                          example of a high-performance tablet detecting an electrostatic signal. Unlike the type of
                          capacitive design used for touchscreens, the Scriptel design is able to detect the position
                          of the pen while it is in proximity to, or hovering above, the tablet.

touch            A basic touchscreen has three main components: a touch sensor, a controller, and a software
screen           driver. The touchscreen is an input device, so it needs to be combined with a display and a PC or
                 other device to make a complete touch input system.

                 1. Touch Sensor

Mike Ross BCC 2008                                                                                               Page 10
Computer Science – Notes for Components - Stages 2 & 3

                 A touch screen sensor is a clear glass panel with a touch responsive surface. The touch
                 sensor/panel is placed over a display screen so that the responsive area of the panel covers the
                 viewable area of the video screen. There are several different touch sensor technologies on the
                 market today, each using a different method to detect touch input. The sensor generally has an
                 electrical current or signal going through it and touching the screen causes a voltage or signal
                 change. This voltage change is used to determine the location of the touch to the screen.

                 2. Controller
                 The controller is a small PC card that connects between the touch sensor and the PC. It takes
                 information from the touch sensor and translates it into information that PC can understand. The
                 controller is usually installed inside the monitor for integrated monitors or it is housed in a plastic
                 case for external touch add-ons/overlays. The controller determines what type of
                 interface/connection you will need on the PC. Integrated touch monitors will have an extra cable
                 connection on the back for the touchscreen. Controllers are available that can connect to a
                 Serial/COM port (PC) or to a USB port (PC or Macintosh). Specialized controllers are also available
                 that work with DVD players and other devices.

                 3. Software Driver
                 The driver is a software update for the PC system that allows the touchscreen and computer to
                 work together. It tells the computer's operating system how to interpret the touch event
                 information that is sent from the controller. Most touch screen drivers today are a mouse-
                 emulation type driver. This makes touching the screen the same as clicking your mouse at the same
                 location on the screen. This allows the touchscreen to work with existing software and allows new
                 applications to be developed without the need for touchscreen specific programming. Some
                 equipment such as thin client terminals, DVD players, and specialized computer systems either do
                 not use software drivers or they have their own built-in touch screen driver.
                 also see

bar    code
                 Barcode reader

                 A typical handheld barcode scanner

                 A barcode reader (or barcode scanner) is an electronic device for reading printed barcodes. Like a
                 flatbed scanner, it consists of a light source, a lens and a photo conductor translating optical
                 impulses into electrical ones. Additionally, nearly all barcode readers contain decoder circuitry
                 analyzing the barcode's image data provided by the photo conductor and sending the barcode's
                 content to the scanner's output port. Types of barcode readers

Mike Ross BCC 2008                                                                                                 Page 11
Computer Science – Notes for Components - Stages 2 & 3


                 Scanning methods are distinguished by the amount of operator manipulation required:

                        Pen type readers: requires the operator to swipe the pen over the code.
                        Semi-automatic handheld readers: The operator need not swipe, but must at least
                         position the reader near the label
                        Fix-mount readers for automatic reading: The reading is performed laterally passing the
                         label over the reader. No operator is required, but the position of the code target must
                         coincide with the imaging capability of the reader and ll
                        Reader gates for automatic scanning: The position of the code must be just under the gate
                         for short time, enabling the scanner sweep to capture the code target successfully.

                 Types of technology

                 The reader types can be distinguished as follows:

                        Pen type readers

                         Pen type readers consist of a light source and a photodiode that are placed next to each
                         other in the tip of a pen or wand. To read a bar code, the tip of the pen moves across the
                         bars in a steady motion. The photodiode measures the intensity of the light reflected back
                         from the light source and generates a waveform that is used to measure the widths of the
                         bars and spaces in the bar code. Dark bars in the bar code absorb light and white spaces
                         reflect light so that the voltage waveform generated by the photo diode is a
                         representation of the bar and space pattern in the bar code. This waveform is decoded by
                         the scanner in a manner similar to the way Morse code dots and dashes are decoded.

                        Laser scanners

                         Laser scanners work the same way as pen type readers except that they use a laser beam
                         as the light source and typically employ either a reciprocating mirror or a rotating prism to
                         scan the laser beam back and forth across the bar code. As with the pen type reader, a
                         photodiode is used to measure the intensity of the light reflected back from the bar code.
                         In both pen readers and laser scanners, the light emitted by the reader is tuned to a
                         specific frequency and the photodiode is designed to detect only this modulated light of
                         the same frequency.

                        CCD Readers

                         CCD readers (also referred to as LED scanner) use an array of hundreds of tiny light
                         sensors lined up in a row in the head of the reader. Each sensor can be thought of as a
                         single photodiode that measures the intensity of the light immediately in front of it. Each
                         individual light sensor in the CCD reader is extremely small and because there are
                         hundreds of sensors lined up in a row, a voltage pattern identical to the pattern in a bar
                         code is generated in the reader by sequentially measuring the voltages across each sensor
                         in the row. The important difference between a CCD reader and a pen or laser scanner is
                         that the CCD reader is measuring emitted ambient light from the bar code whereas pen or
                         laser scanners are measuring reflected light of a specific frequency originating from the
                         scanner itself.

                        Camera-Based Readers

                         2D imaging scanners are the fourth and newest type of bar code reader currently

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Computer Science – Notes for Components - Stages 2 & 3

                         available. They use a small video camera to capture an image of a bar code. The reader
                         then uses sophisticated digital image processing techniques to decode the bar code. Video
                         cameras use the same CCD technology as in a CCD bar code reader except that instead of
                         having a single row of sensors, a video camera has hundreds of rows of sensors arranged
                         in a two dimensional array so that they can generate an image.
                         There are a number of open source libraries for barcode reading from images. These
                         include the ZXing project, which reads one- and two-dimensional barcodes using Android
                         and JavaME, the JJIL project, which includes code for reading EAN-13 barcodes from
                         cellphone cameras using J2ME, and Zebra, which reads various one-dimensional barcodes
                         in C. Even web site integration, either by image uploads (e.g. Folke Ashberg: EAN-13
                         Image-Scanning and code creation tools) or by use of plugins (e.g. the Barcodepedia uses a
                         flash application and some web cam for querying a database), have been realized options
                         for resolving the given tasks.

                 Housing Types

                 The reader packaging can be distinguished as follows:

                        Handheld scanner : with a handle and typically a trigger button for switching on the light
                        Pen scanner (or wand scanner) : a pen-shaped scanner that is swiped.
                        Stationary scanner : wall- or table-mounted scanners that the barcode is passed under or
                         beside. These are commonly found at the checkout counters of supermarkets and other
                        Fixed position scanner : an industrial barcode reader used to identify products during
                         manufacture or logistics. Often used on conveyor tracks to identify cartons or pallets
                         which need to be routed to another process or shipping location. Another application joins
                         holographic scanners with a checkweigher to read bar codes of any orientation or
                         placement, and weighs the package. Systems like this are used in factory and farm
                         automation for quality management and shipping.
                        PDA scanner : a PDA with a built-in barcode reader or attached barcode scanner e.g.
                        Automatic reader : a back office equipment to read barcoded documents at high speed
                         (50,000/hour) e.g. Multiscan MT31

                 Methods of networking

                 Wireless networking

                 Modern handheld barcode readers are operated in wireless networks according to IEEE 802.11g
                 (WLAN) or IEEE 802.15.3 (Bluetooth). However, such configuration limits the time of operation
                 from battery or rechargeable battery and required recharging at least after a shift of operation.

                 Types of connectors

                 PS/2 port

                 Most barcode readers use a PS/2 or USB cable for output: PS/2 cables are connected to the host
                 computer in a Y formation, the PS/2 keyboard port with its first end, to the keyboard with its
                 second, and to the barcode reader with its third end. The barcode characters are then received by
                 the host computer as if they came from its keyboard decoded and converted to keyboard input

Mike Ross BCC 2008                                                                                             Page 13
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                 within the scanner housing. This makes it easy to interface the bar code reader to any application
                 that is written to accept keyboard input.

                 Many readers can also be equipped with an RS-232 output port so that the decoded characters
                 arrive at the computer via one of its RS-232 connectors. A program called a "Software Wedge"
                 takes the data from the bar code reader and feeds it to the application where the data has to go.

                 USB is supported by many newer scanners. In many cases a choice of USB interface types (HID,
                 CDC) are provided.

                 There are a few other less common interfaces. Wand emulation is another output type that takes
                 the raw wave and decodes it, normalizing the output so it can be easily decoded by the host device.
                 Wand emulation can also convert symbologies that may not be recognized by the host device into
                 another symbology (typically Code 39) that can be easily decoded.


                 The scanner resolution is measured by the size of the dot of light emitted by the reader. If this dot
                 of light is wider than any bar or space in the bar code, then it will overlap two elements (two spaces
                 or two bars) and it may produce wrong output. On the other hand, if a too small dot of light is used,
                 then it can misinterpret any spot on the bar code making the final output wrong.

                 The most commonly used dimension is 13 mils (0.3302 mm). As it is a very high resolution, it is
                 extremely important to have bar codes created with a high resolution graphic application.

                 While cell phone cameras are not suitable for many traditional barcodes, there are 2D barcodes
                 (such as Semacode) which are optimized for cell phones. These open up a number of applications
                 for consumers:

                         Movies: DVD/VHS movie catalogs
                         Music: CD catalogs, play MP3 when scanned
                         Book catalogs
                         Groceries, nutrition information, making shopping lists when the last of an item is used,
                         Personal Property inventory (for insurance and other purposes)
                         Calling cards: 2D barcodes can store contact information for importing.
                         Brick and mortar shopping: Portable scanners can be used to record items of interest for
                          looking up online at home.
                         Coupon management: weeding expired coupons.
                         Personal finance. Receipts can be tagged with a barcode label and the barcode scanned
                          into personal finance software when entering. Later, scanned receipt images can then be
                          automatically associated with the appropriate entries. Later, the bar codes can be used to
                          rapidly weed out paper copies not required to be retained for tax or asset inventory
                         If retailers put barcodes on receipts that allowed downloading an electronic copy or
                          encoded the entire receipt in a 2D barcode, consumers could easily import data into
                          personal finance, property inventory, and grocery management software. Receipts
                          scanned on a scanner could be automatically identified and associated with the
                          appropriate entries in finance and property inventory software.


                 There are currently four different types of bar code readers available. Each uses a slightly different
                 technology for reading and decoding a bar code. There are pen type readers (e.g. bar code wands),

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                 laser scanners, CCD readers and camera-based readers.

                 Pen Type Readers and Laser Scanners

                 Pen type readers consist of a light source and a photo diode that are placed next to each other in
                 the tip of a pen or wand. To read a bar code, you drag the tip of the pen across all the bars in a
                 steady even motion. The photo diode measures the intensity of the light reflected back from the
                 light source and generates a waveform that is used to measure the widths of the bars and spaces in
                 the bar code. Dark bars in the bar code absorb light and white spaces reflect light so that the
                 voltage waveform generated by the photo diode is an exact duplicate of the bar and space pattern
                 in the bar code. This waveform is decoded by the scanner in a manner similar to the way Morse
                 code dots and dashes are decoded.

                 Laser scanners work the same way as pen type readers except that they use a laser beam as the
                 light source and typically employ either a reciprocating mirror or a rotating prism to scan the laser
                 beam back and forth across the bar code. Just the same as with the pen type reader, a photo diode
                 is used to measure the intensity of the light reflected back from the bar code. In both pen readers
                 and laser scanners, the light emitted by the reader is tuned to a specific frequency and the photo
                 diode is designed to detect only this same frequency light.

                 Pen type readers and laser scanners can be purchased with different resolutions to enable them to
                 read bar codes of different sizes. The scanner resolution is measured by the size of the dot of light
                 emitted by the reader. The dot of light should be equal to or slightly smaller than the narrowest
                 element width ("X" dimension). If the dot is wider than the width of the narrowest bar or space,
                 then the dot will overlap two or more bars at a time thereby causing the scanner to not be able to
                 distinguish clear transitions between bars and spaces. If the dot is too small, then any spots or
                 voids in the bars can be misinterpreted as light areas also making a bar code unreadable. The most
                 commonly used X dimension is 13 mils (roughly 4 printer dots on a 300 DPI printer). Because this X
                 dimension is so small, it is extremely important that the bar code is created with a program that
                 creates high resolution graphics (like B-Coder). For a good description of the different graphic file
                 formats that are commonly used to create bar codes see: Raster vs. Vector Graphics

                 CCD Readers

                 CCD (Charge Coupled Device) readers use an array of hundreds of tiny light sensors lined up in a
                 row in the head of the reader. Each sensor can be thought of as a single photo diode that measures
                 the intensity of the light immediately in front of it. Each individual light sensor in the CCD reader is
                 extremely small and because there are hundreds of sensors lined up in a row, a voltage pattern
                 identical to the pattern in a bar code is generated in the reader by sequentially measuring the
                 voltages across each sensor in the row. The important difference between a CCD reader and a pen
                 or laser scanner is that the CCD reader is measuring emitted ambient light from the bar code
                 whereas pen or laser scanners are measuring reflected light of a specific frequency originating from
                 the scanner itself.

                 Camera-Based Readers

                 The fourth and newest type of bar code reader currently available are camera-based readers that
                 use a small video camera to capture an image of a bar code. The reader then uses sophisticated
                 digital image processing techniques to decode the bar code. Video cameras use the same CCD
                 technology as in a CCD bar code reader except that instead of having a single row of sensors, a
                 video camera has hundreds of rows of sensors arranged in a two dimensional array so that they can
                 generate an image.

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                 The factors that make a bar code readable are: an adequate print contrast between the light and
                 dark bars and having all bar and space dimensions within the tolerances for the symbology. It is
                 also helpful to have sharp bar edges, few or no spots or voids, a smooth surface and clear margins
                 or "quiet zones" at either end of the printed symbol.

                 Interfacing a bar code reader to a PC

                 All application programs support bar code reading as long as you have the right equipment. Bar
                 code readers are available with two types of output - either "keyboard wedge" output or RS232
                 output. The bar code readers with keyboard wedge output plug directly into the keyboard port on
                 your PC and they also provide a pigtail connector so that you can plug in your keyboard at the same
                 time. When you scan a bar code with the keyboard wedge bar code reader, the data goes into the
                 computer just as if it were typed in on the keyboard. This makes it extremely easy to interface the
                 bar code reader to any application that is written to accept keyboard data.

                 The keyboard wedge interface is extremely simple however it has a few drawbacks. If you swipe a
                 bar code, the cursor has to be in the correct input field in the correct application otherwise you end
                 up reading bar code data into whatever application has the focus. This can cause all sorts of
                 potential problems as you can imagine. The keyboard output also is limited in that you cannot
                 modify the data in any way before sending it into the program that is to receive the data. For
                 example, if you needed to parse a bar code message into multiple pieces or remove some of a bar
                 code message or add in a date or time stamp you would not be able to with a normal keyboard
                 wedge reader.

                 The other possible output option is to get a bar code reader with an RS232 or "Serial" interface.
                 With these types of bar code readers, you connect the reader to an available serial port on the back
                 of your PC. You would then need a program called a "Software Wedge" to take the data from the
                 bar code reader and feed it to the application where you want the data to go. The disadvantage to
                 this approach is that it is a little more complex however you gain much more control over how and
                 where your data ends up when you read a bar code.


                 Also see

RFID reader
                 RFID Reader

                 An RFID reader is a device that is used to interrogate an RFID tag. The reader has an antenna that
                 emits radio waves; the tag responds by sending back its data.

                 A number of factors can affect the distance at which a tag can be read (the read range). The
                 frequency used for identification, the antenna gain, the orientation and polarization of the reader
                 antenna and the transponder antenna, as well as the placement of the tag on the object to be
                 identified will all have an impact on the RFID system’s read range.


                 How RFID Works

                 How does RFID work? A Radio-Frequency IDentification system has three parts:

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                         A scanning antenna
                         A transceiver with a decoder to interpret the data
                         A transponder - the RFID tag - that has been programmed with information.

                 The scanning antenna puts out radio-frequency signals in a relatively short range. The RF radiation
                 does two things:

                         It provides a means of communicating with the transponder (the RFID tag) AND
                         It provides the RFID tag with the energy to communicate (in the case of passive RFID tags).

                 This is an absolutely key part of the technology; RFID tags do not need to contain batteries, and can
                 therefore remain usable for very long periods of time (maybe decades).

                 The scanning antennas can be permanently affixed to a surface; handheld antennas are also
                 available. They can take whatever shape you need; for example, you could build them into a door
                 frame to accept data from persons or objects passing through.

                 When an RFID tag passes through the field of the scanning antenna, it detects the activation signal
                 from the antenna. That "wakes up" the RFID chip, and it transmits the information on its microchip
                 to be picked up by the scanning antenna.

                 In addition, the RFID tag may be of one of two types. Active RFID tags have their own power source;
                 the advantage of these tags is that the reader can be much farther away and still get the signal.
                 Even though some of these devices are built to have up to a 10 year life span, they have limited life
                 spans. Passive RFID tags, however, do not require batteries, and can be much smaller and have a
                 virtually unlimited life span.

                 RFID tags can be read in a wide variety of circumstances, where barcodes or other optically read
                 technologies are useless.

                         The tag need not be on the surface of the object (and is therefore not subject to wear)
                         The read time is typically less than 100 milliseconds
                         Large numbers of tags can be read at once rather than item by item.


                 RFID Basics - How Does RFID Work?

                 RFID is an acronym for "radio-frequency identification" and refers to a technology whereby digital
                 data encoded in RFID tags or smart labels (defined below) are captured by a reader via radio waves.
                 RFID is similar to barcoding in that data from a tag or label are captured by a device that stores the
                 data in a database. RFID, however, has several advantages over tracking systems that use barcodes.
                 The most notable is that RFID tag data can be read outside the line-of-sight, whereas barcodes
                 must be aligned with an optical scanner.

                 How Does RFID Work?

                 RFID belongs to a group of technologies referred to as Automatic Identification and Data Capture
                 (AIDC). AIDC methods automatically identify objects, collect data about them, and enter those data
                 directly into computer systems with little or no human intervention.

                 RFID methods utilize radio waves to accomplish this. At a simple level, RFID systems consist of three
                 components: an RFID tag or smart label, an RFID reader, and an antenna. RFID tags contain an

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                 integrated circuit and an antenna, which are used to transmit data to the RFID reader (also called
                 an interrogator). The reader then converts the radio waves to a more usable form of data.
                 Information collected from the tags is then transferred through a communications interface to a
                 host computer system, where the data can be stored in a database and analyzed at a later time.

                 RFID Tags and Smart Labels

                 As stated above, an RFID tag consists of an integrated circuit and an antenna. The tag is also
                 composed of a protective material that holds the pieces together and shields them from various
                 environmental conditions. The protective material depends on the application. For example,
                 employee ID badges containing RFID tags are typically made from durable plastic, and the tag is
                 embedded between the layers of plastic. RFID tags come in a variety of shapes and sizes and are
                 either passive or active. Passive tags are the most widely used, as they are smaller and less
                 expensive to implement. Passive tags must be "powered up" by the RFID reader before they can
                 transmit data. Unlike passive tags, active RFID tags have an on-board power supply (e.g., a battery),
                 thereby enabling them to transmit data at all times. For a more detailed discussion, refer to this
                 article: Passive RFID Tags vs. Active RFID Tags.

                 Smart labels differ from RFID tags in that they incorporate both RFID and barcode technologies.
                 They're made of an adhesive label embedded with an RFID tag inlay, and they may also feature a
                 barcode and/or other printed information. Smart labels can be encoded and printed on-demand
                 using desktop label printers, whereas programming RFID tags is more time consuming and requires
                 more advanced equipment.

                 RFID Applications

                 RFID technology is employed in many industries to perform such tasks as:

                 - Inventory management
                 - Asset tracking
                 - Personnel tracking
                 - Controlling access to restricted areas
                 - ID badging
                 - Supply chain management
                 - Counterfeit prevention (e.g., in the pharmaceutical industry)

                 Although RFID technology has been in use since World War II, the demand for RFID equipment is
                 increasing rapidly, in part due to mandates issued by the U.S. Department of Defense (DoD) and
                 Wal-Mart requiring their suppliers to enable products to be traceable by RFID.

                 Whether or not RFID compliance is required, applications that currently use barcode technology
                 are good candidates for upgrading to a system that uses RFID or some combination of the two.
                 RFID offers many advantages over the barcode, particularly the fact that an RFID tag can hold much
                 more data about an item than a barcode can. In addition, RFID tags are not susceptible to the
                 damages that may be incurred by barcode labels, like ripping and smearing.


                 What is a Microphone?

                 A microphone is an electromechanical device that uses vibration to create an electrical signal
                 proportional to the vibration, which is usually an air pressure wave. There are many different types

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                 of microphone, ranging from the old condensers to the modern piezoelectrics.

                 Microphon History

                 Alexander Graham Bell invented the first microphone in 1876 as part of the telephone. Thomas
                 Edison invented the first carbon microphone in 1886, a significant improvement on Bell's
                 impractical liquid microphone, and the forerunner of the modern microphone.

                 Microphone Types

                 Condenser microphones are a capacitor that has a fixed plate and a moving plate plate connected
                 to a diaphragm. Air vibrations cause the diaphragm plate to move slightly and change the voltage
                 between the plates. The electret microphone is a modern improvement on the old condenser
                 design, and uses a dielectric material that has a permanently static charge, eliminating the need for
                 a power supply to maintain the charge. This allows electrets to be made very small and cheap.

                 Dynamic microphones have a coil connected to a diaphragm that moves between a fixed
                 permanent magnet. Vibration causes the diaphragm and coil to move, inducing a current in the coil
                 proportional to the vibration. It is the opposite process of creating sound with a speaker, and while
                 speakers can be used as microphones, their signal quality is poor.

                 Carbon microphones have a fixed plate and a moving plate connected to a diaphragm. Between the
                 plates are tiny carbon grains that move when the diaphragm is vibrated. This movement changes
                 the total contact surface area of the carbon, which also changes the resistance between the plates.
                 The changing resistance results in voltage changes proportional to the vibration.

                 Ribbon microphones use the movement of a thin metal foil suspended in a magnetic field to create
                 a signal. Piezoelectric microphones convert vibration into mechanical stress to create a charge from
                 the piezoelectric crystal.

                 Sound Direction

                 Microphones are also categorized according to how well they pick up sound from certain
                 directions. Omni-directionals detect sound equally well from all angles, bi-directionals pickup from
                 the front and back but not the sides, and uni-directionals only pick up sound from the front.

                 Microphone Applications

                 Microphones are commonly used in television, radio, concerts, telephones, and public address
                 systems, but also in other unusual applications. They have been used by rescuers to find survivors
                 after disasters, and by police to conduct surveillance. They are used for feedback in noise
                 cancellation systems, and used to detect the vibrations that precede volcanoes and earthquakes.

                 See also

                 Video capture

                 Video capture is the process of converting an analog video signal—such as that produced by a
                 video camera or DVD player—to digital form. The resulting digital data are referred to as a digital

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                 video stream, or more often, simply video stream. This is in contrast with screencasting, in which
                 previously digitized video is captured while displayed on a digital monitor.

                 Capture process

                 The video capture process involves several processing steps. First the analog video signal is digitized
                 by an analog-to-digital converter to produce a raw, digital data stream. In the case of composite
                 video, the luminance and chrominance are then separated; this is not necessary for S-Video
                 sources. Next, the chrominance is demodulated to produce colour difference video data. At this
                 point, the data may be modified so as to adjust brightness, contrast, saturation and hue. Finally,
                 the data is transformed by a colour space converter to generate data in conformance with any of
                 several colour space standards, such as RGB and YCbCr. Together, these steps constituted video
                 decoding, because they "decode" an analog video format such as NTSC or PAL.

                 Hardware Special electronic circuitry is required to capture video from analog video sources. At the
                 system level this function is typically performed by a dedicated video capture card. Such cards
                 often utilize video decoder integrated circuits to implement the video decoding process.


                 An example of the use of Vid-Caps is the recently released trailer for Activision's Call of Duty 4:
                 Modern Warfare. Within hours of the trailer being aired during the NFL Draft on April 28, 2007,
                 websites such as Planet CallofDuty had posted several versions of the 1 minute 37 second trailer so
                 that fans of the Call of Duty series could attempt to extrapolate new features and facets of the


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                Computer Monitors

                   The computer monitor is an output device that is part of your computer's display system. A
                cable connects the monitor to a video adapter (video card) that is installed in an expansion slot on
                your computer’s motherboard. This system converts signals into text and pictures and displays
                them on a TV-like screen (the monitor).

                The computer sends a signal to the video adapter, telling it what character, image or graphic to
                display. The video adapter converts that signal to a set of instructions that tell the display device
                (monitor) how to draw the image on the screen.

                Cathode Ray Tube (CRT)
                The CRT, or Cathode Ray Tube, is the "picture tube" of your monitor. Although it is a large vacuum
                tube, it's shaped more like a bottle. The tube tapers near the back where there's a negatively
                charged cathode, or "electron gun". The electron gun shoots electrons at the back of the positvely
                charged screen, which is coated with a phosphorous chemical. This excites the phosphors causing
                them to glow as individual dots called pixels (picture elements). The image you see on the
                monitor's screen is made up of thousands of tiny dots (pixels). If you've ever seen a child's LiteBrite
                toy, then you have a good idea of the concept. The distance between the pixels has a lot to do with
                the quality of the image. If the distance between pixels on a monitor screen is too great, the picture
                will appear "fuzzy", or grainy. The closer together the pixels are, the sharper the image on screen.
                The distance between pixels on a computer monitor screen is called its dot pitch and is measured
                in millimeters. (see sidebar). You should try to get a monitor with a dot pitch of .28 mm or less.

                Note: From an environmental point of view, the monitor is the most difficult computer peripheral
                to dispose of because of the lead it contains.

                There are a couple of electromagnets (yokes) around the collar of
                the tube that actually bend the beam of electrons. The beam scans
                (is bent) across the monitor from left to right and top to bottom to
                create, or draw the image, line by line. The number of times in one
                second that the electron gun redraws the entire image is called the
                refresh rate and is measured in Hertz (Hz).
                If the scanning beam hits each and every line of pixels, in succession,
                on each pass, then the monitor is known as a non-interlaced
                monitor. A non-interlaced monitor is preferred over an interlaced
                monitor. The electron beam on an interlaced monitor scans the odd
                numbered lines on one pass, then scans the even lines on the
                second pass. This results in an almost imperceivable flicker that can cause eye-strain.

                This type of eye-strain can result in blurred vision, sore eyes, headaches and even nausea. Don't

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                buy an interlaced monitor, they can be a real pain in the ... ask your optometrist.

                Interlaced computer monitors are getting harder to find (good!), but they are still out there, so
                keep that in mind when purchasing a monitor and watch out for that "steal of a deal".

                Video Technologies
                   Video technologies differ in many different ways. However, the major 2 differences are
                resolution and the number of colours it can produce at those resolutions.

                   Resolution is the number of pixels that are used to draw an image on the screen. If you could
                count the pixels in one horizontal row across the top of the screen, and the number of pixels in one
                vertical column down the side, that would properly describe the resolution that the monitor is
                displaying. It’s given as two numbers. If there were 800 pixels across and 600 pixels down the side,
                then the resolution would be 800 X 600. Multiply 800 times 600 and you’ll get the number of pixels
                used to draw the image (480,000 pixels in this example). A monitor must be matched with the
                video card in the system. The monitor has to be capable of displaying the resolutions and colours
                that the adapter can produce. It works the other way around too. If your monitor is capable of
                displaying a resolution of 1,024 X 768 but your adapter can only produce 640 X 480, then that’s all
                you’re going to get.
                   When we talk about the different technologies, we’re talking about the video card and monitor
                that make up that display system. Also, standards describe the basic number of colours and
                resolutions for each technology, but individual manufacturers always take liberties, providing
                options and enhancements that are designed to make their product more appealing to the end
                user. This is, of course, how new standards come about.

                    Monochrome monitors are very basic displays that produce only one colour. The basic text
                mode in DOS is 80 characters across and 25 down. When graphics were first introduced, they were
                fairly rough by todays standards, and you had to manually type in a command to change from text
                mode to graphics mode. A company called Hercules Graphics developed a video adapter that could
                do this for you. Not only could it change from text to graphics, but it could do it on the fly whenever
                the application required it. Today’s adapters still basically use the same methods.

                   The Colour Graphics Adapter (CGA) introduced colour to the personal computer. In APA mode it
                can produce a resolution of 320 X 200 and has a palette of 16 colours but can only display 4 at a
                time. With the introduction of the IBM Enhanced Graphics Adapter (EGA), the proper monitor was
                capable of a resolution of 640 X 350 pixels and could display 16 colours from a palette of 64.

                    Up until VGA, colours were produced digitally. Each electron beam could be either on or off.
                There were three electron guns, one for each colour, red, green and blue (RGB). This combination
                could produce 8 colours. By cutting the intensity of the beam in half, you could get 8 more colours
                for a total of 16. IBM came up with the idea of developing an analog display system that could
                produce 64 different levels of intensity. Their new Video Graphics Array adapter was capable of a
                resolution of 640 X 480 pixels and could display up to 256 colours from a palette of over 260,000.
                This technology soon became the standard for almost every video card and monitor being

                    Once again, manufacturers began to develop video adapters that
                added features and enhancements to the VGA standard. Super-VGA is
                based on VGA standards and describes display systems with several
                different resolutions and a varied number of colours. When SVGA first
                came out it could be defined as having capabilities of 800 X 600 with

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                256 colours or 1024 X 768 with 16 colours. However, these cards and monitors are now capable of
                resolutions up to 1280 X 1024 with a palette of more than 16 million colours.

                    Extended Graphics Array was developed by IBM. It improved upon the VGA standard (also
                developed by IBM) but was a proprietary adapter for use in Micro Channel Architecture expansion
                slots. It had its own coprocessor and bus-mastering ability, which means that it had the ability to
                execute instructions independent of the CPU. It was also a 32-bit adapter capable of increased data
                transfer speeds. XGA allowed for better performance, could provide higher resolution and more
                colours than the VGA and SVGA cards at the time. However, it was only available for IBM machines.
                Many of these features were later incorporated by other video card manufacturers.


                Also see
printer         In computing, a printer is a peripheral which produces a hard copy (permanent human-readable
                text and/or graphics) of documents stored in electronic form, usually on physical print media such
                as paper or transparencies. Many printers are primarily used as local peripherals, and are attached
                by a printer cable or, in most newer printers, a USB cable to a computer which serves as a
                document source. Some printers, commonly known as network printers, have built-in network
                interfaces (typically wireless or Ethernet), and can serve as a hardcopy device for any user on the
                network. Individual printers are often designed to support both local and network connected users
                at the same time.

                In addition, a few modern printers can directly interface to electronic media such as memory sticks
                or memory cards, or to image capture devices such as digital cameras, scanners; some printers are
                combined with a scanners and/or fax machines in a single unit, and can function as photocopiers.
                Printers that include non-printing features are sometimes called Multifunction Printers (MFP),
                Multi-Function Devices (MFD), or All-In-One (AIO) printers. Most MFPs include printing, scanning,
                and copying among their features.

                Printers are designed for low-volume, short-turnaround print jobs; requiring virtually no setup time
                to achieve a hard copy of a given document. However, printers are generally slow devices (30 pages
                per minute is considered fast; and many consumer printers are far slower than that), and the cost-
                per-page is relatively high. The printing press remains the machine of choice for high-volume,
                professional publishing. However, as printers have improved in quality and performance, many jobs
                which used to be done by professional print shops are now done by users on local printers; see
                desktop publishing. The world's first computer printer was a 19th century mechanically driven
                apparatus invented by Charles Babbage for his Difference Engine.


                also see


                How does a Laser Printer Work?

                A laser printer is so-called because a laser beam is essential in its operations. It is also distinct from
                other printers because of its great printing speeds as well as highly accurate rendering. For
                instance, there are laser printers in the market that can print a hundred coloured pages and two

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                hundred non-coloured pages every minute.

                Components of a Laser Printer

                A basic laser printer assembly has six main components. The first one is the image processor with
                its own memory. This image processor is programmed to convert text data into raster images which
                are then stored, ready for processing and printing.

                The other basic components of a laser printer are the charged roller or charged corona wire, a
                photosensitive drum (a conveyor-like contraption), negatively charged toner, a fuser assembly and,
                of course, the laser assembly.

                The Process of Printing

                The first step to the printing process is the transmission of the data from the computer or data
                storage device to the printer's image processor. The image processor rasterizes the data and
                converts the information received into a graphic image (this is complete in colour and formatting
                information if applicable); this image is then sent to the printer's memory in preparation for

                Meanwhile, the photosensitive drum is revolving and touching the charged roller or the charged
                corona wire. The wire or the roller imparts its negative charge to the drum and the latter acquires a
                negative static charge, as a result. This static charge remains on the drum's surface as long as it's

                At this point, the laser assembly beams light on to the revolving photocell. The laser beam passes
                through a series of focusing mirrors so that it would hit the drum precisely. This laser beam is
                activated and triggered by the data stored in the image processor memory.

                At the points of the drum hit by the laser beam, the charge is reversed from negative to positive
                (since these areas have been exposed to light, they can no longer keep their negative charges).
                Through this process, the image is outlined and drawn on the drum by the laser beam; that is, the
                positively-charged portions of the revolving drum or photocell represent the complete image of the
                text or picture to be printed.

                Now, the drum or the photocell touches the negatively charged toner (fine coloured or black, dry
                powder). This toner clings to all the positively charged portions of the photocell and leaves all the
                negatively charged portions alone. At this point, the photocell bears the actual image.

                Next, the photocell or the drum rolls over the paper and the toner is transferred to the latter. The
                paper with toner then passes through the fuser assembly which bonds the toner particles to the
                paper. Through a combination of heat (coming from a heat source within the fuser's tube) and
                pressure, the toner powder (made of wax or other easy to melt substance) melts on and gets
                bonded with the paper. The paper then comes out printed.


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                A plotter is a type of printer. It's used to make design drawings (architectural, engineering and so
                on). Most of them are called Pen Plotters because they use pens to draw the pictures.

                For example, they may hold pens that draw with ink, in widths of 0.18, 0.25, 0.35, 0.5, 0.7 and
                1mm. Or they may have a few coloured ink pens. The pens are held in a carrier, with the ends
                capped to stop them drying out. When the pen is needed, the head unloads the pen it already has,
                then loads the new pen. This is held perpendicular to the paper or film that will be drawn on.

                The plotter is controlled by simple plotting commands such as

                         Get 0.5 black
                         Go to 267, 899
                         Pen down
                         Go to 267, 801
                         Go to 247, 801
                         Pen up
                         Draw circle 120, 130, 20
                         Pen up
                         Pen home

                The plotters that predated the PC
                era used a type of BASIC control
                language. These were the first
                "printers" that HP made.

                Plotters are also called XY
                Plotters because they work in X
                and Y coordinates. They are
                typically used as the output of CAD (computer aided design/drafting) programs. However,
                nowadays inkjet printers are much faster and easier to use for most applications.

                Plotters can also be used with a cutting head to make things such as adhesive signs.

                Up to a certain size the plotter has a flat bed to hold the paper, and the pen moves in X and Y
                directions. (Also called flat-bed plotter). Above a certain size it's easier and more compact to load
                the paper so that it hand over a roller. The pen only moves in X axis and the paper moves in the Y
                axis. Although it mightn't seem like it, this is how a standard inkjet printer works. Plotters are
                characterised by the maximum size paper they hold. For instance, A2, which is the same size as four

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                A4 sheets put together, or A0 which is like 16 A4 sheets.


                A device that draws pictures on paper based on commands from a computer. Plotters differ from
                printers in that they draw lines using a pen. As a result, they can produce continuous lines, whereas
                printers can only simulate lines by printing a closely spaced series of dots. Multicolour plotters use
                different-coloured pens to draw different colours.

                In general, plotters are considerably more expensive than printers. They are used in engineering
                applications where precision is mandatory.


                See also

                                              Cross sectional views of a typical speaker

                A Speaker is actually a linear motor

                Loudspeakers are really very simple devices from an operational standpoint. An amplifier generates
                electrical energy that alternates constantly from positive to negative in a pattern of waves that vary
                in size and frequency. The output from the amplifier is connected to the speaker at the Terminal
                Strip. There is a fine braided wire that carries the signal from the terminals to the conductors
                leading to the Voice Coil Assembly. These wires are extremely flexible, to enable the Cone to move
                back and forth without restriction or stress, and to do so without breaking these wires. The Voice

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                coil itself is mounted on a rigid cylinder, to which it is firmly glued.
                All the moving parts operate as a single unit, and are suspended by the surround, or outer edge of
                the cone at the front, and by the "Spider" at the rear. At it's natural resting point, the voice coil is
                centered within a narrow magnetic Field Gap. This gap constitutes the north and south poles of the
                Magnet Structure, whose energy is derived from a powerful permanent Magnet sandwiched
                between the two pole pieces. Essentially, the speaker operates by responding to positive and
                negative waves from the amplifier, passing through the voice coil, causing it to be moved back and
                forth by attraction to one pole of the magnet, and repulsion by the other. Since the voice coil is
                rigidly mounted to the cone, the resulting energy is transmitted to the cone producing a piston like
                motion that alternately compresses and evacuates the adjacent air, thus producing sound. If there
                is a high degree of conformity between the original recorded sound, and the sound produced from
                the speaker system as a whole, we then have high fidelity. If we do this for two channels of discrete
                sound information, we have stereo, and if there are four or more channels being activated, we
                have surround sound.

                Things that make a difference in speaker quality

                The operating principles that make a typical speaker work today are identical to those used one
                hundred years ago for the same purpose. The most obvious difference that might be noticed
                between those first speakers and common units today, is the replacement of the electrical field coil
                used to create the magnetic field in those early units, by a powerful, permanent (non-electrical)
                magnet made from highly refined metallurgical materials. Gauss density, which is a measure of the
                strength of magnets, is many times higher in modern alloys. The higher the gauss density, the
                greater the field strength. This is the force within the speaker motor that principally determines the
                amount of power from the amplifier that the speaker will be able to handle.
                Another important factor used to assess power handling, is the weight of the magnet itself, which
                usually has a bearing on the amount of magnetic energy it can produce.


                See also

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primary storage
                               See for data on storage
        RAM,        Random-access memory (usually known by its acronym, RAM) is a form of computer
                     data storage. Today it takes the form of integrated circuits that allow the stored data to
                     be accessed in any order (i.e., at random). The word random thus refers to the fact that
                     any piece of data can be returned in a constant time, regardless of its physical location
                     and whether or not it is related to the previous piece of data.

                     This contrasts with storage mechanisms such as tapes, magnetic discs and optical discs,
                     which rely on the physical movement of the recording medium or a reading head. In
                     these devices, the movement takes longer than the data transfer, and the retrieval time
                     varies depending on the physical location of the next item.

                     The word RAM is mostly associated with volatile types of memory (such as DRAM
                     memory modules), where the information is lost after the power is switched off.
                     However, many other types of memory are RAM as well (i.e., Random Access Memory),
                     including most types of ROM and a kind of flash memory called NOR-Flash.


                     An early type of widespread writable random access memory was the magnetic core
                     memory, developed in 1949-1951, and subsequently used in most computers up until
                     the development of the static and dynamic integrated RAM circuits in the late 1960s and
                     early 1970s. Before this, computers used relays, delay lines or various kinds of vacuum
                     tube arrangements to implement "main" memory functions (i.e., hundreds or thousands
                     of bits), some of which were random access, some not. Latches built out of vacuum tube
                     triodes, and later, out of discrete transistors, were used for smaller and faster memories
                     such as registers and (random access) register banks. Prior to the development of
                     integrated ROM circuits, permanent (or read-only) random access memory was often
                     constructed using semiconductor diode matrices driven by address decoders.

                     Types of RAM

                     Modern types of writable RAM generally store a bit of data in either the state of a flip-
                     flop, as in SRAM (static RAM), or as a charge in a capacitor (or transistor gate), as in
                     DRAM (dynamic RAM), EPROM, EEPROM and Flash. Some types have circuitry to detect
                     and/or correct random faults called memory errors in the stored data, using parity bits
                     or error correction codes. RAM of the read-only type, ROM, instead uses a metal mask
                     to permanently enable/disable selected transistors, instead of storing a charge in them.

                     As both SRAM and DRAM are volatile, other forms of computer storage, such as disks
                     and magnetic tapes, have been used as "permanent" storage in traditional computers.
                     Many newer products instead rely on flash memory to maintain data between sessions
                     of use: examples include PDAs, small music players, mobile phones, synthesizers,
                     advanced calculators, industrial instrumentation and robotics, and many other types of
                     products; even certain categories of personal computers, such as the OLPC XO-1, Asus
                     Eee PC, and others, have begun replacing magnetic disk with so called flash drives
                     (similar to fast memory cards equipped with an IDE or SATA interface).

                     There are two basic types of flash memory: the NOR type, which is capable of true
                     random access, and the NAND type, which is not; the former is therefore often used in
                     place of ROM, while the latter is used in most memory cards and solid-state drives, due

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                     to a lower price.

                     Memory hierarchy

                     Many computer systems have a memory hierarchy consisting of CPU registers, on-die
                     SRAM caches, external caches, DRAM, paging systems, and virtual memory or swap
                     space on a hard drive. This entire pool of memory may be referred to as "RAM" by many
                     developers, even though the various subsystems can have very different access times,
                     violating the original concept behind the random access term in RAM. Even within a
                     hierarchy level such as DRAM, the specific row, column, bank, rank, channel, or
                     interleave organization of the components make the access time variable, although not
                     to the extent that rotating storage media or a tape is variable. (Generally, the memory
                     hierarchy follows the access time with the fast CPU registers at the top and the slow
                     hard drive at the bottom.)

                     In many modern personal computers, the RAM comes in an easily upgraded form of
                     modules called memory modules or DRAM modules about the size of a few sticks of
                     chewing gum. These can quickly be replaced should they become damaged or too small
                     for current purposes. As suggested above, smaller amounts of RAM (mostly SRAM) are
                     also integrated in the CPU and other ICs on the motherboard, as well as in hard-drives,
                     CD-ROMs, and several other parts of the computer system. The overall goal of using a
                     memory hierarchy is to obtain the higher possible average access performance while
                     minimizing the total cost of entire memory system.


                     If a computer becomes low on RAM during intensive application cycles, the computer
                     can perform an operation known as "swapping". When this occurs, the computer
                     temporarily uses hard drive space as additional memory. Constantly relying on this type
                     of backup memory is called thrashing, which is generally undesirable because it lowers
                     overall system performance. In order to reduce the dependency on swapping, more
                     RAM can be installed.

                     Other uses of the "RAM" term

                     Other physical devices with read/write capability can have "RAM" in their names: for
                     example, DVD-RAM. "Random access" is also the name of an indexing method: hence,
                     disk storage is often called "random access" because the reading head can move
                     relatively quickly from one piece of data to another, and does not have to read all the
                     data in between. However the final "M" is crucial: "RAM" (provided there is no
                     additional term as in "DVD-RAM") always refers to a solid-state device.

                     RAM disks

                     Software can "partition" a portion of a computer's RAM, allowing it to act as a much
                     faster hard drive that is called a RAM disk. Unless the memory used is non-volatile, a
                     RAM disk loses the stored data when the computer is shut down. However, volatile
                     memory can retain its data when the computer is shut down if it has a separate power
                     source, usually a battery.

                     Shadow RAM

                     Sometimes, the contents of a ROM chip are copied to SRAM or DRAM to allow for
                     shorter access times (as ROM may be slower). The ROM chip is then disabled while the
                     initialized memory locations are switched in on the same block of addresses (often

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                     write-protected). This process, sometimes called shadowing, is fairly common in both
                     computers and embedded systems.

                     As a common example, the BIOS in typical personal computers often has an option
                     called “use shadow BIOS” or similar. When enabled, functions relying on data from the
                     BIOS’s ROM will instead use DRAM locations (most can also toggle shadowing of video
                     card ROM or other ROM sections). Depending on the system, this may or may not result
                     in increased performance. On some systems the benefit may be hypothetical because
                     the BIOS is not used after booting in favour of direct hardware access. Of course,
                     somewhat less free memory is available when shadowing is enabled


                     also see
        ROM,        Read-Only Memory or ROM is an integrated-circuit memory chip that contains
                     configuration data. ROM is commonly called firmware because its programming is fully
                     embedded into the ROM chip. As such, ROM is a hardware and software in one.

                     Because datais fully incorporated at the ROM chip's manufacture, data stored can
                     neither be erased nor replaced. This means permanent and secure data storage .
                     However, if a mistake is made in manufacture, a ROM chip becomes unusable. The most
                     expensive stage of ROM manufacture, therefore, is creating the template. If a template
                     is readily available, duplicating the ROM chip is very easy and affordable.

                     A ROM chip is also non volatile so data stored in it is not lost when power is turned off.

                     RAM versus ROM

                     Both RAM and ROM provide the user random access to stored data. However, RAM
                     provides only short-term memory since data stored in RAM is lost when power is turned
                     off. ROM, on the other hand, provides long-term storage since data is permanently
                     etched into the ROM chip.

                     One other difference between the two is that RAM's data can frequently and speedily be
                     altered and changed at will. ROM cannot be reconfigured at all.

                     ROM Chip Manufacture

                     The ROM chip has a matrix of columns and rows. The point of intersection between the
                     column and the row is called a cell. Each cell will have a value of either 1 or 0. The
                     manufacturer of the ROM chip has to determine each cell's value before the ROM
                     manufacture ensues.

                     After the program has been designed, the ROM chip can now be made. At each cell
                     where the value should be 1, a diode is placed to connect column to row. At each cell
                     where the value should be 0, no diode is placed.

                     The ROM Chip's Diode

                     The diode is the cell's electronic check valve. Its main function in the ROM chip is to
                     control and direct the flow of electric current in cells. Specifically, it transfers the electric

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                     current from column to row.

                     The diode has a minimum voltage requirement, what is commonly called the forward
                     breakover, which needs to be surpassed before the diode will transfer the charge from
                     the column to the row of the cell. The usual ROM diode forward breakover voltage is
                     around 0.6 volts.

                     The ROM activates cells by sending through voltage that is more than the cells' diode
                     forward breakover. The charge that is directed through the column gets passed on by
                     the diode to the appropriate grounded row. Since charge is successfully transmitted
                     from column to row, the cell where a diode is present has a value of 1.

                     In the ROM circuit, passing a charge through the column will not affect the cells whose
                     values are supposed to be 0. In any cell, this charge cannot be passed from column to
                     row if there's no diode to facilitate the transfer. Therefore, once a cell's value has been
                     determined to be 0, it will permanently be 0.


                     also see
        cache       Cache (pronounced cash) memory is extremely fast memory that is built into a
                     computer’s central processing unit (CPU), or located next to it on a separate chip. The
                     CPU uses cache memory to store instructions that are repeatedly required to run
                     programs, improving overall system speed. The advantage of cache memory is that the
                     CPU does not have to use the motherboard’s system bus for data transfer. Whenever
                     data must be passed through the system bus, the data transfer speed slows to the
                     motherboard’s capability. The CPU can process data much faster by avoiding the
                     bottleneck created by the system bus.

                     As it happens, once most programs are open and running, they use very few resources.
                     When these resources are kept in cache, programs can operate more quickly and
                     efficiently. All else being equal, cache is so effective in system performance that a
                     computer running a fast CPU with little cache can have lower benchmarks than a system
                     running a somewhat slower CPU with more cache. Cache built into the CPU itself is
                     referred to as Level 1 (L1) cache. Cache that resides on a separate chip next to the CPU is
                     called Level 2 (L2) cache. Some CPUs have both L1 and L2 cache built-in and designate
                     the separate cache chip as Level 3 (L3) cache.

                     Cache that is built into the CPU is faster than separate cache, running at the speed of the
                     microprocessor itself. However, separate cache is still roughly twice as fast as Random
                     Access Memory (RAM). Cache is more expensive than RAM, but it is well worth getting a
                     CPU and motherboard with built-in cache in order to maximize system performance.

                     Disk caching applies the same principle to the hard disk that memory caching applies to
                     the CPU. Frequently accessed hard disk data is stored in a separate segment of RAM in
                     order to avoid having to retrieve it from the hard disk over and over. In this case, RAM is
                     faster than the platter technology used in conventional hard disks. This situation will
                     change, however, as hybrid hard disks become ubiquitous. These disks have built-in
                     flash memory caches. Eventually, hard drives will be 100% flash drives, eliminating the
                     need for RAM disk


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                     A cache is a type of dynamic and high speed memory that is used to supplement the
                     function of the central processing unit and the physical disk storage. The cache acts as a
                     buffer when the CPU tries to access data from the disk so the data traveling from the
                     CPU and physical disks can have synchronized speed. Disk reading and writing process is
                     generally slower than CPU function.

                     In computer science theory, a cache is any collection of data that duplicates original
                     values which are stored elsewhere in the computer. The original data may be expensive
                     to fetch because of the disparity in access time between components. So a cache can act
                     as a temporary storage where data which are most frequently accessed are stored so
                     fast processing. In future processing, the CPU may just access the duplicated copy
                     instead of getting it from the physical disk storage which is slower and performance can

                     A cache can either be a reserved section in the memory of the computer or a separate
                     storage device with very fast speed. In personal computers, there two common types of
                     caching namely: memory caching and disk caching.

                     A memory cache is sometimes known as RAM cache of cache store. This is a portion of
                     the random access memory (RAM) which is made of high speed static RAM (SRAM).
                     SRAM is faster than the dynamic RAM (DRAM). When computers are executing, most
                     programs access the same data or instructions repetitively so storing these data or
                     instructions in memory cache makes performance effective.

                     Other memory caches are directly built in the main body of the microprocessor. For
                     instance, the old Intel 80486 microprocessor has 8K of memory cache while the Pentium
                     had 16K. The cache as also called Level 1 (L1) caches. Modern computers come with
                     external cache memory which is called Level 2 (L2) cache. The L2 cache is situated
                     between the CPU and the DRAM.

                     On the other hand, disk caching is almost similar to memory caching except that disk
                     cache uses the conventional old memory instead of the high speed SRAM. Frequently
                     accessed data from the disk storage device are stored in the memory buffer. The
                     program first needs to see if there is data from the disk cache before getting data from
                     the hard disk. This method significantly increases performance because access speed in
                     RAM can be as much as thousands of times faster than access speed in hard disks.

                     A cache hit is a term used when data is found in the cache. The cache's effectiveness is
                     determined by its hit rate. A technique known as smart caching is used by many cache
                     systems as well. The technique is able to recognize certain types of data which are being
                     frequently used and automatically caches them.

                     Another kind of cache is the BIND DNS daemon which maps domain names to IP
                     addresses. This makes it easier for numeric IP addresses to be matched faster with their
                     corresponding domain names.

                     Web browsers also employ a caching system of recently viewed web pages. With these
                     caching system, a user will not have to wait to get data from remote servers because the
                     latest pages are on his computer's web cache. A lot of internet service providers user
                     proxy cache for there clients to save on bandwidth in their networks.

                     Some search engines have indexed pages in their cache so when links to these web
                     pages are shown in the search results and the actual website is temporarily offline or

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                     inaccessible, the search engine will give the cached pages to the user.


                                                      What is the CPU Cache?

                     The cache on your CPU has become a very important part of today's computing. The
                     cache is a very high speed and very expensive piece of memory, which is used to speed
                     up the memory retrieval process. Due to its expensive CPU's come with a relatively small
                     amount of cache compared with the main system memory. Budget CPU's have even less
                     cache, this is the main way that the top processor manufacturers take the cost out of
                     their budget CPU's.

                                                  How does the CPU Cache work?

                     Without the cache memory every time the CPU requested data it would send a request
                     to the main memory which would then be sent back across the memory bus to the CPU.
                     This is a slow process in computing terms. The idea of the cache is that this extremely
                     fast memory would store and data that is frequently accessed and also if possible the
                     data that is around it. This is to achieve the quickest possible response time to the CPU.
                     Its based on playing the percentages. If a certain piece of data has been requested 5
                     times before, its likely that this specific piece of data will be required again and so is
                     stored in the cache memory.

                     Lets take a library as an example o how caching works. Imagine a large library but with
                     only one librarian (the standard one CPU setup). The first person comes into the library
                     and asks for Lord of the Rings. The librarian goes off follows the path to the bookshelves
                     (Memory Bus) retrieves the book and gives it to the person. The book is returned to the
                     library once its finished with. Now without cache the book would be returned to the
                     shelf. When the next person arrives and asks for Lord of the Rings, the same process
                     happens and takes the same amount of time.

                     If this library had a cache system then once the book was returned it would have been
                     put on a shelf at the librarians desk. This way once the second person comes in and asks
                     for Lord of the Rings, the librarian only has to reach down to the shelf and retrieve the
                     book. This significantly reduces the time it takes to retrieve the book. Back to computing
                     this is the same idea, the data in the cache is retrieved much quicker. The computer uses
                     its logic to determine which data is the most frequently accessed and keeps them books
                     on the shelf so to speak.

                     That is a one level cache system which is used in most hard drives and other
                     components. CPU's however use a 2 level cache system. The principles are the same.
                     The level 1 cache is the fastest and smallest memory, level 2 cache is larger and slightly
                     slower but still smaller and faster than the main memory. Going back to the library,
                     when Lord of the Rings is returned this time it will be stored on the shelf. This time the
                     library gets busy and lots of other books are returned and the shelf soon fills up. Lord of
                     the Rings hasn't been taken out for a while and so gets taken off the shelf and put into a
                     bookcase behind the desk. The bookcase is still closer than the rest of the library and
                     still quick to get to. Now when the next person come in asking for Lord of the Rings, the
                     librarian will firstly look on the shelf and see that the book isn't there. They will then
                     proceed to the bookcase to see if the book is in there. This is the same for CPU's. They
                     check the L1 cache first and then check the L2 cache for the data they require.


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Secondary storage
     magnetic,      All hard drives share the same basic structure, varying only in how each part is used and
                     the quality of the parts themselves. The platters, spindle motor, heads, and head
                     actuator are inside the drive, all sealed from the outside environment. This chamber is
                     often called the head disk assembly (HDA). The HDA is rarely opened, except by
                     professionals. On the outside are the logic board, bezel, and mounting equipment.
                     Below, I will describe each of these components.

                     The platters are the disks inside the drive. Platters can vary in size. Often the size of the
                     drive, 5.25″ or 3.5″, is based on the physical size of the platters. Most drives several
                     platters. They are usually made of an aluminum alloy so that they are light. The newest
                     and largest drives make use of a new technology of glass/ceramic platters. Basically, this
                     is glass with enough ceramic within to resist cracking. This glass technology is taking
                     over aluminum in the hard drive industry. Many popular manufacturers already use it,
                     including Maxtor, Toshiba, and SeaGate. Glass platters can be made much thinner than
                     aluminum ones, they can better resist the heat produced during operation and they are
                     also better able to withstand the extreme centrifugal forces during spinning on the
                     spindle. The platters are mounted onto a spindle in the interior of the HDA.

                     Alone, platters are not capable of recording data. Each one is coated with a film of some
                     magnetically sensitive substance. The oxide media is one of the older ways of doing this.
                     With this, a mixture of compound syrup is poured onto the platter, then spun to evenly
                     distribute the film over the entire platter. This substance has iron oxide as a main
                     ingredient, explaining why many platters you may see will be brownish-orange. Using an
                     oxide coating developed limits over time as capacities increased. Whats more, the oxide
                     medium could not survive a head crash at all, and usually this required drive
                     replacement. The more modernly used media consists of a thin film of a cobalt alloy
                     which is placed on the platter through electroplating, much like chrome. This media is
                     then coated with a thin layer of protective substance to allow some measure of
                     protection against head crash. Overall, this new medium is much flatter at the
                     microscopic level, allowing the heads to run closer to the platter (more on this in a bit).

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                     The read/write heads do just that, they read and write to the platters. There is usually
                     one head per platter side, and each head is attached to a single actuator shaft so that all
                     the heads move in unison. Each head is spring loaded to force it into the platter it reads.
                     When off, each head rests on the platter surface. When the drive is running, the
                     spinning of the platters causes air pressure that lifts the heads ever-so-slightly off the
                     platter surface. The distance between the head and platter is very small…so small that
                     the HDA must be assembled in a clean room because one dust particle can throw the
                     whole thing off. This sensitivity and accuracy is what causes only bigger companies to be
                     able to repair hard drives simply because of the expense of a clean room. A slider is
                     attached to each head. This mechanism actually glides over the platter and holds the
                     head at the correct distance to do its job. You can see a full head assembly to the right.
                     You can see the sliders on the end of each head.

                     Air flow inside of the drive plays an important part in overall operation. In fact, air is
                     what holds the heads off of the platters while the drive is on. The rotation of the platters
                     creates an air flow. The heads fly like an airplane on this cusion of air. The air is dragged
                     along with the platters by friction. The high pressure air between the heads and platters
                     form what is called an air bearing. The concept is similar to a hockey puck gliding over an
                     air hockey table.


                     Inside a hard drive

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                         1.   Actuator (compact electric motor that moves the read-write arm).
                         2.   Read-write arm swings read-write head back and forth across platter.
                         3.   Central spindle allows platter to rotate at high speed.
                         4.   Magnetic platter stores information in binary form.
                         5.   Plug connections link hard drive to circuit board in personal computer.
                         6.   Read-write head is a tiny magnet on the end of the read-write arm.
                         7.   Circuit board on underside controls the flow of data to and from the platter.
                         8.   Flexible connector carries data from circuit board to read-write head and
                         9.   Small spindle allows read-write arm to swing across platter.


                     Also see

        optical     optical storage refers to any storage device that uses laser light technology
                     to retrieve and store data. CD-ROM drives, CD players and DVD players are the most
                     popular consumer electronics that fall under this category. By now, every household in
                     America contains at least a CD player, and DVD is quickly gaining steam.

                     Today, just about every PC has a CD-ROM drive, and now we are going to find out
                     exactly how it works. Unlike magnetic storage devices (hard drives, floppy disks, ZIP
                     drives, etc) a majority of optical storage devices are "Read Only", meaning that they can
                     be read from, but cannot be written to. Over the last few years, we have seen an
                     insurgence in the market of "writable" and "re-writable" CD-ROM devices. These devices
                     are capable of both writing to, and reading from optical disks. However, writing data
                     with optical devices is time consuming, more technically challenging, and less reliable
                     than recording with magnetic storage. Once the data is written, however, nothing short
                     of physically damaging the disc will destroy the data.

                     Initially, the music and software industry was very opposed to the sale of Re-Writable
                     CD-ROM drives, or "CD Burners" as they are commonly called. Concerns were raised
                     about the usage of these devices for piracy. Nevertheless, the CD-R/W drive has become

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                     one of the most popular computer components sold and installed into consumer
                     computer systems.

                     Humble beginnings in a big place
                     Sony and Philips joined forces in 1978 to cooperate on the development of current CD
                     technology. Philips was already working on an optical storage medium, and Sony
                     brought a ton of experience in digital recording. Initially the two companies were poised
                     for a battle to create competing standards but they inked an agreement for a
                     cooperative development project to create a single standard.

                     Sony originally wanted to use a 12 inch platter for the new optical disc (the same size as
                     a standard vinyl LP), but Philips wanted to investigate smaller disc sizes, especially after
                     they discovered that they could pack up to 12 hours of music onto a single 12 inch disk!
                     Needless to say, this was overkill. The average music album is normally just over 1 hour

                     A 12 inch Laser Disc (LD) was also developed. The LD saw duty as a format for movie
                     playback, and was used in Laser Disc based arcade games such as Dragon's Lair and
                     Space Ace.

                     The LD failed to catch on as a mainstream replacement for the VHS video tape (this
                     honor was reserved for DVD), but it did capture a niche market among audiophiles, who
                     went to LD for its enhanced visual and sound quality. Movies are still being sold today in
                     Laser Disc format, but are only produced in limited quantities.

                     By 1982, the final Compact Disc standard was released. The standard included
                     specification details for recording, sampling, and most importantly the familiar 4.72-inch
                     diameter disc size. Legend has it that the size was chosen because it was large enough to
                     contain the entire of Beethoven's 70 minute "Ninth Symphony" without interruption.
                     The final format of the disc would be capable of holding 74 minutes (approx 650MB) of
                     audio or data, with a small amount of space reserved for error correction and other

                     Sony and Philips continued to cooperate through the 80's, as they announced and
                     introduced new refinements to the technology and new standards, including the familiar
                     CD-ROM drive.

                     The Disc
                     The Compact Disc itself is made of a polycarbonate (plastic) wafer 1.2mm thick with a
                     15mm hole in the center for mounting to the playback device. The actual data is stored
                     on a thin aluminum film, or "strata" that is "punched" with the digital data, and then
                     covered with another protective plastic layer. The disc is read from by a low power laser
                     beam, which penetrates the protective surface and reads the data from aluminum
                     surface the disc. The disc is spun at varying rotational speeds depending on the disc
                     encoding method, and location of the data being read.

                     A special LED (Light Emitting Diode) is used to generate the laser beam, which passes
                     through a beam splitter. A small, computer

                     controlled electric motor is used to move and position the laser lens head in the correct
                     position to read the required data. A photo-detector picks up the reflections of the laser
                     beam and interprets the data. A strong reflection indicates, "land" while a diffused or
                     weak reflection indicates a "pit." In digital terms, the weak reflection of the pit is
                     interpreted as a logical high, or 1. A strong reflection of land is interpreted as a logical

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                        low, or 0. These signals are then passed through a DAC (Digital To Analog Converter)
                        circuit that translates the digital data into analog data. That information is then passed
                        to the amplifier unit, which then amplifies the sound and sends it out to the speakers.

                        A CD is only readable from one side. A label is placed on the other so that you know
                        which side is the data side of the disc. Even with the protective plastic coating, the disc is
                        still just plastic, and as such can be easily scratched or gouged if mishandled. The CD
                        player is able to cope with small scratches, but larger scratches will cause music to skip
                        during playback, or may even render the disc completely unreadable. Smudges from
                        fingerprints and dirt can be easily wiped off, but a scratch is pretty much permanent.
                        Ironically, most folks tend to end up scratching the disk in an attempt to clean off
                        smudges because they used a cloth and/or cleaner that was too abrasive.


                        Also see

        Flash Memory   Flash memory refers to a particular type of EEPROM, or Electronically Erasable
                        Programmable Read Only Memory. It is a memory chip that maintains stored
                        information without requiring a power source.

                        Flash memory differs from EEPROM in that EEPROM erases its content one byte at a
                        time. This makes it slow to update. Flash memory can erase its data in entire blocks,
                        making it a preferable technology for applications that require frequent updating of
                        large amounts of data as in the case of a memory stick.

                        Inside the flash chip, information is stored in cells. A floating gate protects the data
                        written in each cell. Tunneling electrons pass through a low conductive material to
                        change the electronic charge of the gate in "a flash," clearing the cell of its contents so
                        that it can be rewritten. This is how flash memory gets its name.

                        Flash memory is very useful in a variety of applications including:

                                Your computer BIOS
                                Memory sticks
                                PCMCIA memory cards
                                MP3 players
                                Modems
                                Video game cards
                                Digital cellular phones
                                Digital cameras

                        Flash memory used as a hard drive has many advantages over a traditional hard drive.
                        It's nonvolatile or solid state, meaning there are no moving parts. It's also silent, much
                        smaller than a traditional hard drive, and highly portable with a much faster access time.
                        However, the advantages of a traditional hard drive are price and capacity. Hard drives
                        are many times larger for a price that is many times smaller, comparatively speaking,
                        megabyte for megabyte.

                        That said, the price of flash memory continues to drop as capacity continues to rise,
                        making it a prize candidate for an ever-broadening set of applications.

Mike Ross BCC 2008                                                                                             Page 38
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                     Note: Flash memory is not the same thing as flash RAM (Random Access Memory). Flash
                     RAM, like any type of RAM in your computer, requires a continual power source to
                     maintain its contents.


                     Also see

        DAT         DAT (Digital Audio Tape) is a standard medium and technology for the digital recording
                     of audio on tape at a professional level of quality. A DAT drive is a digital tape recorder
                     with rotating heads similar to those found in a video deck. Most DAT drives can record
                     at sample rates of 44.1 kHz, the CD audio standard, and 48 kHz. DAT has become the
                     standard archiving technology in professional and semi-professional recording
                     environments for master recordings. Digital inputs and outputs on professional DAT
                     decks allow the user to transfer recordings from the DAT tape to an audio workstation
                     for precise editing. The compact size and low cost of the DAT medium makes it an
                     excellent way to compile the recordings that are going to be used to create a CD master.

                     As an archiving medium, DAT is an alternative to consider along with:

                             Digital Data Storage (DDS1 through DDS3)
                             optical disc
                             VHS tape


Mike Ross BCC 2008                                                                                        Page 39
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        buses
        data bus    A collection of wires in which data is transmitted from one computer to another external
                     drive. In personal computers, the data bus refers to internal bus. This is a bus that connects
                     the internal computer components to the CPU and main memory. A bus is a common wire
                     connecting various points in a circuit; examples are the ground bus and power bus. The
                     data bus carries digital information.

                     A data bus is a group of wires connecting different parts of a circuit with wire carrying a
                     different signal. The data bus is connected to the inputs of several gates and to the outputs
                     of several gates. A data bus may be time multiplexed to serve different functions at
                     different times. At any time only one gate may drive information onto the bus line but
                     several gates may receive it. In general, information may flow on the bus wires in both
                     directions. This type of bus is referred to as a bidirectional data bus.

                     There are two types of data bus; they are address bus and a data bus. The data bus
                     transfers data and address bus transfers information about where the data should go. A bus
                     which allows data to be transferred faster, which makes applications run faster. The local
                     bus is of high-speed that connects directly to the processor. Many military systems are
                     compatible with the 1553, but most new commercial systems are not. This system is used
                     for command and telemetry transfer between military spacecraft components, subsystems
                     and instruments, and within complex components themselves.

                     VME is a 32-bit architecture with a 40 Mb/s throughput. Peripheral Component
                     Interconnect (PCI) Bus PCI is in widespread use in the computer industry. Although PCI was
                     developed by Intel, it is not tied to any specific processor. It appears that PCI may
                     eventually replace the older ISA bus and is competing with VME for industrial use. PCI can
                     be 32 or 64-bits wide. It has peak transfer rates of 132 Mb/s, with a sustained transfer rates
                     around 25 Mb/s. The PCI standard is maintained by the PCI Manufacturers although it is an
                     open interface, only 3 or 4 manufacturers actually produce to it. The larger board size,
                     requiring more volume than the other types of interfaces that have smaller form factors.
                     The bus architecture which is developed by IBM for the PC/XT and PC/AT and adopted for
                     industrial applications.

                     The main function of the data bus is to carry digital information. A data bus can be viewed
                     as a group of wires connecting different parts of a circuit with wire carrying a different
                     signal. The data bus is connected to the inputs of several gates and to the outputs of
                     several gates. A data bus may be time multiplexed to serve different functions at different
                     times. The ISA architecture which is also developed by IBM is used for defector standard,
                     and is widely used for high performance. Thus, the main function of the data bus is to
                     connect the system to the external devices. There are many types of data bus, which can
                     connect the PC to the mobile and other external device in order to download software’s.
                     Thus data bus is a media which is transfer the data from one place to another.


                     The width and clock rate of the data bus determine its data rate (the number of bytes per
                     second it can carry), which is one of the main factors determining the processing power of a
                     computer. Most current processor designs use a 32-bit bus, meaning that 32 bits of data
                     can be transferred at once. Some processors have an internal data bus which is wider than
                     their external bus in order to make external connections cheaper while retaining some of
                     the benefits in processing power of a wider bus.


                     How does a Data bus work? Data is represented as groups of 8 bits at a time. A collection of

Mike Ross BCC 2008                                                                                           Page 40
Computer Science – Notes for Components - Stages 2 & 3

                       8 bits is called a byte. A data bus is simply a channel or pipeline through which these bits
                       can pass on their way from one location in the computer to another. The wider the bus, the
                       more bits can be packed side by side and sent at the same time, much as cars travelling a
                       highway can be driven side by side, as long as each car has its own lane to travel along.
                       Most personal computer systems today have a data bus width of 32 bits; in other words
                       they have the ability to send 32 bits at a time from one location to another.
                       Imagine, for example, that we wish to send a lower-case letter 'a' to a printer. The
                       character 'a', being data, has to have a representation within the machine so that the
                       computer knows how to recognise it - using an agreed standard called ASCII, it has been
                       decided that the letter that we know as a lower-case 'a' will be represented within the
                       computer as a pattern of 8 bits: 01100101.

                       Thus the lower-case letter 'a' is represented within the machine by the byte 01100101.
                       Now imagine that we are on an overhead walkway looking down on an 8-lane highway.
                       That a '1' is represented by a car, and that a '0' is represented by the absence of a car. As
                       the byte 01100101 passes beneath us, we would see the following traffic pattern:

                       For a bus width of 32 bits, we would simply have a highway four times wider.


        address bus   An address bus is a computer bus, controlled by CPUs or DMA-capable peripherals for
                       specifying the physical addresses of computer memory elements that the requesting unit
                       wants to access (read or write).

                       The width of an address bus, along with the size of addressable memory elements,
                       generally determines how much memory can be directly accessed. For example, a 16-bit
                       wide address bus (commonly used in the 8-bit processors of the 1970s and early 1980s)
                       reaches across 2 (65,536) memory locations , whereas a 32-bit address bus (common in
                       PC processors as of 2004) can address 2 (4,294,967,296) locations. Some microprocessors,
                       such as the Digital/Compaq Alpha 21264 and Alpha 21364 have an address bus that is
                       narrower than the amount of memory they can address. The address bus is clocked faster
                       than the system or memory bus, enabling it to transfer an address in the same amount of
                       time as an address bus of the same width as the address.

                       In most microcomputers such addressable "locations" are 8-bit bytes, conceptually at least.
                       In such case the above examples translate to 64 kilobytes (KB) and 4 gigabytes (GB)
                       respectively. However, it should be noted that accessing an individual byte frequently
                       requires reading or writing the full bus width (a word) at once. In these instances the least
                       significant bits of the address bus may not even be implemented - it is instead the
                       responsibility of the controlling device to isolate the individual byte required from the

Mike Ross BCC 2008                                                                                              Page 41
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                     complete word transmitted. This is the case, for instance, with the VESA Local Bus which
                     lacks the two least significant bits, limiting this bus to aligned 32 bit transfers.

                     Historically, there were also some examples of computers which were only able to address
                     larger words, such as 36 or 48 bits long.


                     Introduction to the concept of a bus

                     A bus, in computing, is a set of physical connections (cables, printed circuits, etc.) which can
                     be shared by multiple hardware components in order to communicate with one another.

                     The purpose of buses is to reduce the number of "pathways" needed for communication
                     between the components, by carrying out all communications over a single data channel.
                     This is why the metaphor of a "data highway" is sometimes used.

                     If only two hardware components communicate over the line, it is called a hardware port
                     (such as a serial port or parallel port).

                     Characteristics of a bus

                     A bus is characterised by the amount of information that can be transmitted at once. This
                     amount, expressed in bits, corresponds to the number of physical lines over which data is
                     sent simultaneously. A 32-wire ribbon cable can transmit 32 bits in parallel. The term
                     "width" is used to refer to the number of bits that a bus can transmit at once.

                     Additionally, the bus speed is also defined by its frequency (expressed in Hertz), the
                     number of data packets sent or received per second. Each time that data is sent or received
                     is called a cycle.

                     This way, it is possible to find the maximum transfer speed of the bus, the amount of data
                     which it can transport per unit of time, by multiplying its width by its frequency. A bus with
                     a width of 16 bits and a frequency of 133 MHz, therefore, has a transfer speed equal to:

                                 6            6
                     16 * 133.10 = 2128*10 bit/s,
                                 6         6
                     or 2128*10 /8 = 266*10 bytes/s
                               6              3
                     or 266*10 /1000 = 266*10 KB/s
                     or 259.7*10 /1000 = 266 MB/s

                     Bus subassembly

                     In reality, each bus is generally constituted of 50 to 100 distinct physical lines, divided into

Mike Ross BCC 2008                                                                                              Page 42
Computer Science – Notes for Components - Stages 2 & 3

                     three subassemblies:

                            The address bus (sometimes called the memory bus) transports memory addresses
                             which the processor wants to access in order to read or write data. It is a
                             unidirectional bus.
                            The data bus transfers instructions coming from or going to the processor. It is a
                             bidirectional bus.
                            The control bus (or command bus) transports orders and synchronisation signals
                             coming from the control unit and travelling to all other hardware components. It is
                             a bidirectional bus, as it also transmits response signals from the hardware.

                     The primary buses

                     There are generally two buses within a computer:

                            the internal bus (sometimes called the front-side bus, or FSB for short). The
                             internal bus allows the processor to communicate with the system's central
                             memory (the RAM).
                            the expansion bus (sometimes called the input/output bus) allows various
                             motherboard components (USB, serial, and parallel ports, cards inserted in PCI
                             connectors, hard drives, CD-ROM and CD-RW drives, etc.) to communicate with
                             one another. However, it is mainly used to add new devices using what are called
                             expansion slots connected to the input/outpur bus.

                     The chipset

                     A chipset is the component which routes data between the computer's buses, so that all
                     the components which make up the computer can communicate with each other. The
                     chipset originally was made up of a large number of electronic chips, hence the name. It
                     generally has two components:

                            The NorthBridge (also called the memory controller) is in charge of controlling
                             transfers between the processor and the RAM, which is way it is located physically
                             near the processor. It is sometimes called the GMCH, for Graphic and Memory
                             Controller Hub.
                            The SouthBridge (also called the input/output controller or expansion controller)
                             handles communications between peripheral devices. It is also called the ICH (I/O
                             Controller Hub).

                     The tem bridge is generally used to designate a component which connects two buses.

Mike Ross BCC 2008                                                                                        Page 43
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                     It is interesting to note that, in order to communicate, two buses must have the same
                     width. The explains why RAM modules sometimes have to be installed in pairs (for
                     example, early Pentium chips, whose processor buses were 64-bit, required two memory
                     modules each 32 bits wide).

                     Here is a table which gives the specifications for the most commonly used buses:

                     Standard                     Bus width (bits) Bus speed (MHz) Bandwidth (MB/sec)
                     ISA 8-bit                    8                8.3             7.9
                     ISA 16-bit                   16               8.3             15.9
                     EISA                         32               8.3             31.8
                     VLB                          32               33              127.2
                     PCI 32-bit                   32               33              127.2
                     PCI 64-bit 2.1               64               66              508.6
                     AGP                          32               66              254.3
                     AGP (x2 Mode)                32               66x2            528
                     AGP (x4 Mode)                32               66x4            1056
                     AGP (x8 Mode)                32               66x8            2112
                     ATA33                        16               33              33
                     ATA100                       16               50              100
                     ATA133                       16               66              133
                     Serial ATA (S-ATA)           1                                180
                     Serial ATA II (S-ATA2)       2                                380
                     USB                          1                                1.5
                     USB 2.0                      1                                60
                     FireWire                     1                                100
                     FireWire 2                   1                                200
                     SCSI-1                       8                4.77            5
                     SCSI-2 - Fast                8                10              10
                     SCSI-2 - Wide                16               10              20
                     SCSI-2 - Fast Wide 32 bits   32               10              40
                     SCSI-3 - Ultra               8                20              20

Mike Ross BCC 2008                                                                                      Page 44
Computer Science – Notes for Components - Stages 2 & 3

                       SCSI-3 - Ultra Wide          16            20               40
                       SCSI-3 - Ultra 2             8             40               40
                       SCSI-3 - Ultra 2 Wide        16            40               80
                       SCSI-3 - Ultra 160 (Ultra 3) 16            80               160
                       SCSI-3 - Ultra 320 (Ultra 4) 16            80 DDR           320
                       SCSI-3 - Ultra 640 (Ultra 5) 16            80 QDR           640


                       see also

        Control bus   A control bus is (part of) a computer bus, used by CPUs for communicating with other
                       devices within the computer. While the address bus carries the information on which
                       device the CPU is communicating with and the data bus carries the actual data being
                       processed, the control bus carries commands from the CPU and returns status signals from
                       the devices, for example if the data is being read or written to the device the appropriate
                       line (read or write) will be active (logic zero).


                       Control bus is the cable that connects CPU and other devices within the computer to carry
                       control and signalling information, while the data bus carries actual data that is being



Mike Ross BCC 2008                                                                                          Page 45
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Mike Ross BCC 2008                                                                              Page 46
Computer Science – Notes for Components - Stages 2 & 3


   identification of
    for industry

Mike Ross BCC 2008                                                              Page 47
Computer Science – Notes for Components - Stages 2 & 3

   standards in
     storage           A bit is a binary digit, taking a value of either 0 or 1. Binary digits are a basic unit of
        capacities      information storage and communication in digital computing
        (bit, nibble,
        byte,           A four-bit quantity is known as a nibble, and can represent 16 values (2 values, 0–15).
        megabyte,       "Word" is a term for a slightly larger group of bits, but it has no standard size. It represents
        gigabyte,       the size of one register in a Computer-CPU. In the IA-32 architecture more commonly
        terabyte,       known as x86-32, 16 bits are called a "word" (with 32 bits being a double word or dword),
        petabyte)       but other architectures have word sizes of 8, 32, 64, 80 or others.

                        A byte is a basic unit of measurement of information storage in computer science. In many
                        computer architectures it is a unit of memory addressing. There is no standard but a byte
                        most often consists of eight bits. A byte is an ordered collection of bits, with each bit
                        denoting a single binary value of 1 or 0. The byte most often consists of 8 bits in modern
                        systems, however, the size of a byte can vary and is generally determined by the
                        underlying computer operating system or hardware. Historically, byte size was determined
                        by the number of bits required to represent a single character from a Western character
                        set. Its size was generally determined by the number of possible characters in the
                        supported character set and was chosen to be a divisor of the computer's word size.
                        Historically bytes have ranged from five to twelve bits.

                        These are binary units often used with computers. Alternative suggested units are normal
                        base 10 SI prefixes for bytes, i.e. kilobyte = 1,000 bytes, megabyte = 1,000,000 bytes.
                        1 bit is either a 1 or a 0 in the binary language of computers, representative of an electric
                        pulse or lack thereof in a computer circuit. (fact)
                        1 byte is 8 bits - Common characters such as a letter or number typically take up 1 byte.
                        1 kilobyte is 1,024 bytes - An example of a file this size would be a document with roughly
                        200 words.
                        1 megabyte is 1,024 kibibytes - An example of a file this size would be a document with
                        roughly 200,000 words, a very small MP3 audio file, or a short, well compressed video clip.
                        1 gigabyte is 1,024 mebibytes - Older computer systems rarely had more than one
                        gigabyte of hard drive space. One can roughly hold 200 - 300 MP3 files, or a well
                        compressed movie.
                        1 tedibyte is 1,024 gibibytes - Largest amount of space on the market today.
                        1 pebibyte is 1,024 tebibytes - Possibly being used in supercomputers.
                        1 exbibyte is 1,024 pebibytes - Not in existence because there are no known applications
                        for this amount of space.
                        1 zebibyte is 1,024 exbibytes - Not in existence because there are no known applications
                        for this amount of space.
                        1 yobibyte is 1,024 zebibytes - Not in existence because there are no known applications
                        for this amount of space.

        processor      A bus is simply a circuit that connects one part of the motherboard to another. The more
         and      bus   data a bus can handle at one time, the faster it allows information to travel. The speed of
         speeds         the bus, measured in megahertz (MHz), refers to how much data can move across the bus
         (megahertz,    simultaneously.

Mike Ross BCC 2008                                                                                                    Page 48
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                                         Busses connect different parts of the motherboard
                                                          to one another

                     Bus speed usually refers to the speed of the front side bus (FSB), which connects the CPU
                     to the northbridge. FSB speeds can range from 66 MHz to over 800 MHz. Since the CPU
                     reaches the memory controller though the northbridge, FSB speed can dramatically affect
                     a computer's performance.

                     Here are some of the other busses found on a motherboard:

                             The back side bus connects the CPU with the level 2 (L2) cache, also known as
                              secondary or external cache. The processor determines the speed of the back side
                             The memory bus connects the northbridge to the memory.
                             The IDE or ATA bus connects the southbridge to the disk drives.
                             The AGP bus connects the video card to the memory and the CPU. The speed of
                              the AGP bus is usually 66 MHz.
                             The PCI bus connects PCI slots to the southbridge. On most systems, the speed of
                              the PCI bus is 33 MHz. Also compatible with PCI is PCI Express, which is much
                              faster than PCI but is still compatible with current software and operating
                              systems. PCI Express is likely to replace both PCI and AGP busses.

                     The faster a computer's bus speed, the faster it will operate -- to a point. A fast bus speed
                     cannot make up for a slow processor or chipset.


Mike Ross BCC 2008                                                                                           Page 49
Computer Science – Notes for Components - Stages 2 & 3

                     also see

                     CPU speed is not a reliable indicator of CPU performance.

                     Many factors inside and outside of the CPU exert a significant impact on CPU performance,
                     and on overall system performance.

                     The CPU

                     CPU speed is measure in megahertz. A 1MHz CPU can accomplish one million CPU cycles in
                     one second.

                     Does this mean that a 2MHz CPU is twice as fast as a 1Mhz CPU?

                     Not necessarily. This depends on how much work each CPU accomplishes in each clock

                     The 1MHz CPU might very well be faster, in practice, than the 2Mhz CPU - if it is more
                     efficient or can process more tasks in each CPU cycle.

                     The Cache

                     The purpose of a cache is to enable the CPU to access recently used information very

                     A cache will significantly affect CPU performance.

                     However, caches also represent some difficulties in simple comparison.

                     Some caches are bigger than others. A typical L1 cache is 256Kb and a typical L2 cache is

                     Generally speaking, the larger the cache, the better the system performance boost.
                     However, this is not always the case.

                     A cache operates at a certain speed, just like the core of the CPU. Some caches operate at
                     the full speed of the CPU, while others operate at half that speed or less.

                     A small cache which operates at full speed may be much more useful than a cache which is
                     twice as large but operates at only half the speed of the CPU.

                     Even comparing cache sizes can be difficult. Some CPU's utilize inclusive caches. In a CPU
                     with an exclusive cache, the data stored in the L1 cache is often duplicated in the L2 cache.
                     Only CPUs which employ exclusive caches will have the full capacity of their L2 caches

                     The Front Side Bus

                     The Front Side Bus (FSB) is the connection between the CPU and system memory.

                     The Front Side Bus operates at a speed which is a percentage of the CPU clock speed.

Mike Ross BCC 2008                                                                                          Page 50
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                        The faster the speed at which the Front Side Bus allows data transfer, the better the
                        performance of the CPU.

                        System Memory

                        RAM has an access speed. Faster RAM will mean the CPU has to wait less often for data.
                        This will, effectively, make the CPU faster.


                        see also

        graphics       Screen resolution
         (resolution)   Screen resolution refers to the number of pixels a screen can display within a given area.
                        Screen resolution is usually expressed in pixels per linear inch of screen. Most personal
                        computer displays have resolutions that vary from 72 to 96 pixels per inch (ppi). The
                        resolution of the display screen is dependent on how the monitor and display card are
                        configured, but it's safe to assume that most users fall into the lower end of the range, or
                        about 72 to 80 ppi.

                        Images destined for print can be created at various resolutions, but images for Web pages
                        are always limited by the resolution of the computer screen. Thus a square GIF graphic of
                        72 by 72 pixels will be approximately one inch square on a 72-ppi display monitor. When
                        you are creating graphics for Web pages you should always use the 1:1 display ratio (one
                        pixel in the image equals one pixel on the screen), because this is how big the image will
                        display on the Web page. Images that are too large should be reduced in size with a
                        sophisticated image editor like Adobe's Photoshop to display at proper size at a resolution
                        of 72 ppi.


                        The display resolution of a digital television or computer display typically refers to the
                        number of distinct pixels in each dimension that can be displayed. It can be an ambiguous
                        term especially as the displayed resolution is controlled by all different factors in cathode
                        ray tube (CRT) and flat panel or projection displays using fixed picture-element (pixel)

                        One use of the term "display resolution" applies to fixed-pixel-array displays such as
                        plasma display panels (PDPs), liquid crystal displays (LCDs), digital light processing (DLP)
                        projectors, or similar technologies, and is simply the physical number of columns and rows
                        of pixels creating the display (e.g., 1280×1024). A consequence of having a fixed grid
                        display is that for multiformat video inputs all displays need a "scaling-engine" (a digital
                        video processor that includes a memory array) to match the incoming picture format to
                        the display.

                        Note that the use of the word resolution here is misleading. The term "display resolution"
                        is usually used to mean pixel dimensions (e.g., 1280×1024), which does not tell you
                        anything about the resolution of the display on which the image is actually formed (which
                        would typically be given in pixels per inch (digital) or number of lines measured
                        horizontally, per picture height (analog)).

               (further information available)

Mike Ross BCC 2008                                                                                              Page 51
Computer Science – Notes for Components - Stages 2 & 3

                     also see
   components
    from different
   evolution of
   comparing        In computing, measure of the performance of a piece of equipment or software, usually
    performance      consisting of a standard program or suite of programs. Benchmarks can indicate whether a
    using            computer is powerful enough to perform a particular task, and so enable machines to be
    benchmarking.    compared. However, they provide only a very rough guide to practical performance, and
                     may lead manufacturers to design systems that get high scores with the artificial
                     benchmark programs but do not necessarily perform well with day-to-day programs or


                     In computing, a benchmark is the act of running a computer program, a set of programs,
                     or other operations, in order to assess the relative performance of an object, normally by
                     running a number of standard tests and trials against it. The term 'benchmark' is also
                     mostly utilized for the purposes of elaborately-designed benchmarking programs
                     themselves. Benchmarking is usually associated with assessing performance characteristics
                     of computer hardware, for example, the floating point operation performance of a CPU,
                     but there are circumstances when the technique is also applicable to software. Software
                     benchmarks are, for example, run against compilers or database management systems.
                     Another type of test program, namely test suites or validation suites, are intended to
                     assess the correctness of software.

                     Benchmarks provide a method of comparing the performance of various subsystems
                     across different chip/system architectures. Benchmarking is helpful in understanding how
                     the database manager responds under varying conditions. You can create scenarios that
                     test deadlock handling, utility performance, different methods of loading data, transaction
                     rate characteristics as more users are added, and even the effect on the application of
                     using a new release of the product.


                     While some people use their computers mainly for surfing or for work, others are more
                     interested in the performance of their systems or various components. They like to test
                     hardware and sometimes software, not only to see if it lives up to its potential, but also to
                     push it to new heights. There are special tests for this purpose, known as benchmarks.

                     Some computer enthusiasts “overclock” or raise the clock speed to see just how far they
                     can push their systems. Benchmarks are a series of tests used to measure the level of
                     performance at both stock and overclocked speeds. When a system is overclocked, it may
                     not be stable at certain levels, so benchmarks are also used to measure stability at various

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                     People who build their own high performance systems or do a lot of gaming, sometimes
                     run benchmarks to compare scores, competing to see whose system is superior. However,
                     one doesn’t have to over clock in order to use computer benchmark programs.
                     Benchmarks offer a series of graphics and sound tests as well as standardized options,
                     which can also be used to diagnose problems.

                     You can also find multi-tasking benchmarks to see how well your computer holds up under
                     stressful situations. There may be several different processes running at any given time
                     aside from those you are using directly. If you are running more than one program, along
                     with the typical processes, you may notice your computer running slow or lagging as you
                     go back and forth between applications. Multi-tasking benchmarks can help you determine
                     which programs demand the most from your system, and help you establish which if any
                     unnecessary processes you may need to turn off while using high drain applications.

                     There are full system benchmarks as well as those that only test certain parts of a system,
                     such as the memory, CPU function, hard drives, network connections, video cards, and
                     sound cards. You may also be able to purchase plug-in benchmarks for various specialty
                     applications. Benchmark tests can help determine if there is a problem and where it is
                     located. In turn, this may help keep expenses down when having a computer repaired or
                     updated, by establishing that only certain areas require attention.

                     Be careful where you obtain benchmarking programs. Read reviews and choose those
                     offered by reputable companies, even if you have to spend a few bucks. Look for a
                     benchmark program that is easy to use, comes with complete instructions, and explains
                     what scores mean. While you can find a variety of free downloads, some sites that offer
                     benchmarks warn that they can be harmful to your system, so take your time and choose
                     carefully. Check out some overclocking or gaming sites to see what types of benchmarking
                     programs enthusiasts are using and to read reviews.


                     see also

                     Diagnostics programs are different from benchmark programs in that they are very serious
                     programs used to analyse specific computer problems and cure them, instead of only
                     measuring component performance.


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 business           Application software is any tool that functions and is operated by means of a computer,
    application      with the purpose of supporting or improving the software user's work. In other words, is
    software         the subclass of computer software that employs the capabilities of a computer directly and
    (accounting,     thoroughly to a task that the user wishes to perform. This should be contrasted with
    database,        system software (infrastructure) or middleware (computer services/ processes integrators)
    presentation,    is involved in integrating a computer's various capabilities, but typically does not directly
    project          apply them in the performance of tasks that benefit the user. In this context the term
    management,      application refers to both the application software and its implementation.
    word             A simple, if imperfect analogy in the world of hardware would be the relationship of an
    processing)      electric light bulb (an application) to an electric power generation plant (a system). The
                     power plant merely generates electricity, not itself of any real use until harnessed to an
                     application like the electric light that performs a service that benefits the user.

                     Typical examples of software applications are word processors, spreadsheets, and media
                     players, database applications.

                     Multiple applications bundled together as a package are sometimes referred to as an
                     application suite. Microsoft Office,, and iWork 08, which bundle together a
                     word processor, a spreadsheet, and several other discrete applications, are typical
                     examples. The separate applications in a suite usually have a user interface that has some
                     commonality making it easier for the user to learn and use each application. And often
                     they may have some capability to interact with each other in ways beneficial to the user.
                     For example, a spreadsheet might be able to be embedded in a word processor document
                     even though it had been created in the separate spreadsheet application.

                     User-written software tailors systems to meet the user's specific needs. User-written
                     software include spreadsheet templates, word processor macros, scientific simulations,
                     graphics and animation scripts. Even email filters are a kind of user software. Users create
                     this software themselves and often overlook how important it is.

                     In some types of embedded systems, the application software and the operating system
                     software may be indistinguishable to the user, as in the case of software used to control a
                     VCR, DVD player or microwave oven.

                     It is important to note that this definition may exclude some applications that may exist on
                     some computers in large organizations. For an alternate definition of an application: see
                     Application Portfolio Management.


                     The exact delineation between system software such as operating systems and application
                     software is not precise, however, and is occasionally subject to controversy. For example,
                     one of the key questions in the United States v. Microsoft antitrust trial was whether
                     Microsoft's Internet Explorer web browser was part of its Windows operating system or a
                     separable piece of application software. As another example, the GNU/Linux naming
                     controversy is, in part, due to disagreement about the relationship between the Linux
                     kernel and the Linux operating system.

                     In computer science, an application is a computer program designed to help people
                     perform a certain type of work. An application thus differs from an operating system
                     (which runs a computer), a utility (which performs maintenance or general-purpose

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                     chores), and a programming language (with which computer programs are created).
                     Depending on the work for which it was designed, an application can manipulate text,
                     numbers, graphics, or a combination of these elements. Some application packages offer
                     considerable computing power by focusing on a single task, such as word processing;
                     others, called integrated software, offer somewhat less power but include several

                     Application software classification

                     There are many subtypes of application software:

                            Enterprise software addresses the needs of organization processes and data flow,
                             often in a large distributed environment. (Examples include Financial, Customer
                             Relationship Management, and Supply Chain Management). Note that
                             Departmental Software is a sub-type of Enterprise Software with a focus on
                             smaller organizations or groups within a large organization. (Examples include
                             Travel Expense Management, and IT Helpdesk)
                            Enterprise infrastructure software provides common capabilities needed to
                             support Enterprise Software systems. (Examples include Databases, Email servers,
                             and Network and Security Management)
                            Information worker software addresses the needs of individuals to create and
                             manage information, often for individual projects within a department, in
                             contrast to enterprise management. Examples include time management,
                             resource management, documentation tools, analytical, and collaborative. Word
                             processors, spreadsheets, email and blog clients, personal information system,
                             and individual media editors may aid in multiple information worker tasks.
                            Content access software is software used primarily to access content without
                             editing, but may include software that allows for content editing. Such software
                             addresses the needs of individuals and groups to consume digital entertainment
                             and published digital content. (Examples include Media Players, Web Browsers,
                             Help browsers, and Games)
                            Educational software is related to content access software, but has distinct
                             requirements for delivering evaluations (tests) and tracking progress through
                             material. It is also related to collaboration software in that many Educational
                             Software systems include collaborative capabilities.
                            Simulation software are computer software for simulation of physical or abstract
                             systems for either research, training or entertainment purposes.
                            Media development software addresses the needs of individuals who generate
                             print and electronic media for others to consume, most often in a commercial or
                             educational setting. This includes Graphic Art software, Desktop Publishing
                             software, Multimedia Development software, HTML editors, Digital Animation
                             editors, Digital Audio and Video composition, and many others.
                            Product engineering software is used in developing hardware and software
                             products. This includes computer aided design (CAD), computer aided engineering
                             (CAE), computer language editing and compiling tools, Integrated Development
                             Environments, and Application Programmer Interfaces.


                     A word processor (more formally known as document preparation system) is a computer
                     application used for the production (including composition, editing, formatting, and
                     possibly printing) of any sort of printable material.

                     Word processor may also refer to an obsolete type of stand-alone office machine, popular
                     in the 1970s and 80s, combining the keyboard text-entry and printing functions of an

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                     electric typewriter with a dedicated computer for the editing of text. Although features
                     and design varied between manufacturers and models, with new features added as
                     technology advanced, word processors for several years usually featured a monochrome
                     display and the ability to save documents on memory cards or diskettes. Later models
                     introduced innovations such as spell-checking programs, increased formatting options, and
                     dot-matrix printing. As the more versatile combination of a personal computer and
                     separate printer became commonplace, the word processor disappeared.

                     Word processors are descended from early text formatting tools (sometimes called text
                     justification tools, from their only real capability). Word processing was one of the earliest
                     applications for the personal computer in office productivity.

                     Although early word processors used tag-based markup for document formatting, most
                     modern word processors take advantage of a graphical user interface. Most are powerful
                     systems consisting of one or more programs that can produce any arbitrary combination of
                     images, graphics and text, the latter handled with type-setting capability.

                     Microsoft Word is the most widely used computer word processing system; Microsoft
                     estimates over five hundred million people use the Office suite, which includes Word.
                     There are also many other commercial word processing applications, such as WordPerfect,
                     which dominated the market from the mid-1980s to early-1990s, particularly for machines
                     running Microsoft's MS-DOS operating system. Open-source applications such as
                                                                                        [citation needed]
            Writer and KWord are rapidly gaining in popularity.                   Online word
                     processors such as Google Docs are a relatively new category.


                     A spreadsheet is a computer application that simulates a paper worksheet. It displays
                     multiple cells that together make up a grid consisting of rows and columns, each cell
                     containing either alphanumeric text or numeric values. A spreadsheet cell may
                     alternatively contain a formula that defines how the contents of that cell is to be
                     calculated from the contents of any other cell (or combination of cells) each time any cell
                     is updated. Spreadsheets are frequently used for financial information because of their
                     ability to re-calculate the entire sheet automatically after a change to a single cell is made.

                     Visicalc is usually considered the first electronic spreadsheet (although this has been
                     challenged), and it helped turn the Apple II computer into a success and greatly assisted in
                     their widespread application. Lotus 1-2-3 was the leading spreadsheet of DOS era. Excel is
                     now generally considered to have the largest market share.


                     A Computer Database is a structured collection of records or data that is stored in a
                     computer system. The structure is achieved by organizing the data according to a database
                     model. The model in most common use today is the relational model. Other models such
                     as the hierarchical model and the network model use a more explicit representation of
                     relationships (see below for explanation of the various database models).

                     A computer database relies upon software to organize the storage of data. This software is
                     known as a database management system (DBMS). Database management systems are
                     categorized according to the database model that they support. The model tends to
                     determine the query languages that are available to access the database. A great deal of
                     the internal engineering of a DBMS, however, is independent of the data model, and is
                     concerned with managing factors such as performance, concurrency, integrity, and
                     recovery from hardware failures. In these areas there are large differences between

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                     A presentation program is a computer software package used to display information,
                     normally in the form of a slide show. It typically includes three major functions: an editor
                     that allows text to be inserted and formatted, a method for inserting and manipulating
                     graphic images and a slide-show system to display the content.

                     Accounting software is application software that records and processes accounting
                     transactions within functional modules such as accounts payable, accounts receivable,
                     payroll, and trial balance. It functions as an accounting information system. It may be
                     developed in-house by the company or organization using it, may be purchased from a
                     third party, or may be a combination of a third-party application software package with
                     local modifications. It varies greatly in its complexity and cost.

                     The market has been undergoing considerable consolidation since the mid 1990s, with
                     many suppliers ceasing to trade or being bought by larger groups.


                     Project management software is a term covering many types of software,
                     including scheduling, cost control and budget management, resource allocation,
                     collaboration software, communication, quality management and documentation
                     or administration systems, which are used to deal with the complexity of large


                     also see

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   graphics and     In computer graphics, graphics software or image editing software is a program or
    multimedia       collection of programs that enable a person to manipulate visual images on a computer.
                     Computer graphics can be classified into two distinct categories: raster graphics and vector
                     graphics. Before learning about computer software that manipulates or displays these
                     graphics types, you should be familiar with both.

                     Many graphics programs focus exclusively on either vector or raster graphics, but there are
                     a few that combine them in interesting and sometimes unexpected ways. It is simple to
                     convert from vector graphics to raster graphics, but going the other way is harder. Some
                     software attempts to do this.

                     Most graphics programs have the ability to import and export one or more graphics file

                     Several graphics programs support animation, or digital video. Vector graphics animation
                     can be described as a series of mathematical transformations that are applied in sequence
                     to one or more shapes in a scene. Raster graphics animation works in a similar fashion to
                     film-based animation, where a series of still images produces the illusion of continuous


                     Multimedia is media and content that utilizes a combination of different content forms.
                     The term can be used as a noun (a medium with multiple content forms) or as an adjective
                     describing a medium as having multiple content forms. The term is used in contrast to
                     media which only utilize traditional forms of printed or hand-produced material.
                     Multimedia includes a combination of text, audio, still images, animation, video, and
                     interactivity content forms.

                     Multimedia is usually recorded and played, displayed or accessed by information content
                     processing devices, such as computerized and electronic devices, but can also be part of a
                     live performance. Multimedia (as an adjective) also describes electronic media devices
                     used to store and experience multimedia content. Multimedia is similar to traditional
                     mixed media in fine art, but with a broader scope. The term "rich media" is synonymous
                     for interactive multimedia. Hypermedia can be considered one particular multimedia

   CAD,              Computer-aided design (CAD) is the use of computer technology to aid in the design and
                     particularly the drafting (technical drawing and engineering drawing) of a part or product,
                     including entire buildings. It is both a visual (or drawing) and symbol-based method of
                     communication whose conventions are particular to a specific technical field.

                     Drafting can be done in two dimensions ("2D") and three dimensions ("3D"). Drafting is the
                     integral communication of technical or engineering drawings and is the industrial arts sub-
                     discipline that underlies all involved technical endeavors. In representing complex, three-
                     dimensional objects in two-dimensional drawings, these objects have traditionally been
                     represented by three projected views at right angles.

                     Current CAD software packages range from 2D vector-based drafting systems to 3D solid
                     and surface modellers. Modern CAD packages can also frequently allow rotations in three
                     dimensions, allowing viewing of a designed object from any desired angle, even from the
                     inside looking out. Some CAD software is capable of dynamic mathematic modeling, in

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                     which case it may be marketed as CADD — computer-aided design and drafting.

                     CAD is used in the design of tools and machinery used in the manufacture of components,
                     and in the drafting and design of all types of buildings, from small residential types
                     (houses) to the largest commercial and industrial structures (hospitals and factories).

                     CAD is mainly used for detailed engineering of 3D models and/or 2D drawings of physical
                     components, but it is also used throughout the engineering process from conceptual
                     design and layout of products, through strength and dynamic analysis of assemblies to
                     definition of manufacturing methods of components.

                     CAD has become an especially important technology within the scope of computer-aided
                     technologies, with benefits such as lower product development costs and a greatly
                     shortened design cycle. CAD enables designers to lay out and develop work on screen,
                     print it out and save it for future editing, saving time on their drawings.

   desktop          Desktop publishing (also known as DTP) combines a personal computer and WYSIWYG
    publishing,      page layout software to create publication documents on a computer for either large scale
                     publishing or small scale local multifunction peripheral output and distribution.

                     The term "desktop publishing" is commonly used to describe page layout skills. However,
                     the skills and software are not limited to paper and book publishing. The same skills and
                     software are often used to create graphics for point of sale displays, promotional items,
                     trade show exhibits, retail package designs, and outdoor signs.

   image editing    Image editing encompasses the processes of altering images, whether they be digital
                     photographs, traditional analog photographs, or illustrations. Traditional analog image
                     editing is known as photo retouching, using tools such as an airbrush to modify
                     photographs, or editing illustrations with any traditional art medium. Graphic software
                     programs, which can be broadly grouped into vector graphics editors, raster graphics
                     editors, and 3d modelers, are the primary tools with which a user may manipulate,
                     enhance, and transform images. Many image editing programs are also used to render or
                     create computer art from scratch.

   multimedia                               You're browsing to your favorite site on the World Wide Web, and
    authoring,                               as it opens, you notice something has changed. Actually, many
                                             things have. There's a new background color dripping onto your
                                             screen. Animated images catch your eye as they pop to life, while
                                             sound leaps from the page and into and out of your speakers. You
                                             click once, twice, and now you're part of the multimedia
                                             experience. Your clicks cause the animations to flare and the
                                             sounds to erupt. You'll definitely be back to this site.

                     This is a simple example of how multimedia authoring affects our lives as computer users
                     every day. It used to be that multimedia authoring tools were for the elite: professional
                     programmers who created multi-faceted slide shows and sideshows for their corporation's
                     hired actors to take out and use for drumming up sales, marketing clout, and revenue.
                     With the advent of the Web, you don't have to be a pocket-protector-wearing member of
                     the digirati to use multimedia authoring. Some of the tools are still extremely advanced,
                     but anyone who has enough know-how to create a Web site can easily expand their skills
                     enough to making a full-blown multimedia presentation.

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                     We'll talk about the types of presentations you can make, cover the obvious and not so
                     obvious forums for your presentations, and look at the tools available for multimedia

                       What Is Multimedia Authoring?

                     Using an audio- and video-laden presentation has always been an effective method of
                     making your point. If we can see it and hear it, it can affect us. But if we can interact with
                     the presentation in some manner, we have a much greater chance of remembering the
                     information. That's what the authoring aspect of multimedia authoring is all about.
                     Creating a memorable Web site or presentation is more than just slapping a couple of
                     .WAV sound files on top of some lackluster images and calling it multimedia. It has to be
                     something the user (the audience) can become involved in.

                     Doug Dixon, a technology leader at Sarnoff Corp., defines multimedia as "typically at least
                     something visual plus auditory plus interactivity." The sights and sounds are obvious, but
                     adding the interactivity is a bit trickier. "That's the way people regard it now," he says. "In
                     the old days, multimedia was a slide show if you hummed along to it. People can still do it
                     step by step, but now it requires some interaction."

                     This multimedia interactivity can be something simple, such as a click-through slide show
                     with a soundtrack, or much more complicated, such as something involving images, two-
                     dimensional (2-D) animation, video, three-dimensional (3-D) graphics, and and synthesized
                     sound and music, Dixon says.

                       They Call It Multimedia For A Reason

                     We'll get more into the interactivity in a bit, but let's focus first on the easier part: the
                     multimedia. We've already established that this usually means something auditory
                     combined with something visual, but there are many ways to do this.

                     On the visual side, you can have static images or panoramic vistas, linked groups of
                     images, and even virtual worlds of 3-D graphical rendering. Video clips (which you can
                     create digitally or import from your camcorder or VCR) and animation also add much to
                     the visual (although they also add file-size constraints you must consider if you're using
                     video on a Web site or placing it on a CD-ROM).

                     You also can integrate sound effects, recorded quotes, music, and other auditory inputs
                     within the visuals (the audio track that runs with video, for example) or let them stand

                     And although we rarely give it the same glamour level as other forms of multimedia, text
                     often is the most important part of your presentation. The displayed or spoken words
                     mixed with the sounds and images are the heart of the presentation, and you'll want to
                     consider their impact. Different fonts, text styles and sizes, and word placement will affect
                     how easy to read and how memorable your information will be.

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                      Involve The Viewer

                     The best way to make involving presentations is to focus on creating events that stimulate
                     our senses in the same manner as real-world events. For example, a division of Dixon's
                     Sarnoff Corp., VideoBrush, uses Video Mosaic technology to let users create a totally
                     interactive panoramic image. "Video and image mosaics provide a whole new way to
                     enhance multimedia presentations by allowing the user to really see and understand the
                     scene or environment you are trying to present," Dixon says. "Providing full 360-degree
                     panoramas, which the viewer can interactively explore, makes the experience much more

                                                       Users control the viewpoint of these panoramas, which
                                                       users can store in Joint Photographic Experts Group
                                                       (JPEG) format so they're small enough to be used
                                                       efficiently on the Web. By clicking and dragging, users can
                                                       "move" around the world inside the image.

                                                       The Valley Forge Military Academy & College
                                                       ( uses this technology to create a
                                                       virtual tour of its campus. As the user pans past campus
                                                       buildings he or she may want more information about,
                                                       the user can click a specific site and open up a panoramic
                          You can stop in for a        image of the inside of that building or another Web page
                         panoramic view of the         with further information.
                          chapel's interior on
                         your tour of the Valley        So, apart from just having users click through standard
                             Forge Military             hyperlinks, there are many other ways for them to
                          Academy & College             interact. Animation games are another example of a
                                campus.                 quick-and-easy way of making people remember your
                                                        site. Thumbnailing images (images displayed at a fraction
                                                        of their normal size) get users to take the initiative and
                     click pictures they want to see larger, as well as reducing your page's load time.
                     Navigational maps and graphical menus that help users immediately find what they're
                     looking for are another example. You have a number of ways to make your presentations
                     interactive; just make sure the authoring tools you're considering are up to the task.

                      Uses & Tools

                     All this multimedia may be entertaining, but the key point is how it can help advance your
                     business. Multimedia is used for more than just presentations (although that has always
                     been a big part and will likely remain so). It's also useful for marketing, sales, education,
                     employee training, information kiosks, entertainment, and Web sites, Dixon says. Pretty
                     much anywhere you can use images and sounds together (coupled with a dash of
                     interaction, of course), there's a use for multimedia authoring.

                     Multimedia authors come from all areas. "At the high end, there are the creative
                     departments in business. The ones that handle the training and the Web sites," Dixon says.
                     At the other end, "there's the individuals creating business presentations and students
                     building panoramas and simple animations for their Web sites."

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                       When you're ready to start your multimedia ventures, Andy Oeftering, a multimedia
                       course director at Data-Tech Institute says choosing the right tool is the most important
                       step. "The authoring tool that you use defines the capabilities and limits of your
                       presentations, so choose wisely," he says.

                       There are three types of authoring tools, which are divided by the style in which the
                       multimedia presentation is created.

                       Card-based. Sort of like creating notecards for a speech or the standard slide show
                       analogy, card-based authoring tools let you organize the content of your presentation into
                       individual cards or pages. Oeftering says the advantage of card-based programs is their
                       short learning curve. "It's no exaggeration to say you can begin creating multimedia in
                       minutes." But the downside is the difficulty of running media concurrently, he says, since
                       an audio clip must begin and end before another media event can occur.

                       Time-based. Oeftering's metaphor for time-based authoring tools is a reel of film or a
                       multi-track videotape recorder. Tools in this category, such as Macromedia's Director (see
                       below), let you represent your multimedia content along tracks that stretch across
                       individual frames, making it easier to run concurrent media, although also more difficult to

                       Icon-based. Built like a flowchart, icon-based authoring tools let you drag icons from a
                       toolbar to a blank page, Oeftering says. Then, you just double-click an icon, and dialog
                       boxes help you link multimedia activity. These often-expensive programs (up to $5,000)
                       are for applications that rely on interactivity, such as public kiosks (for example, as the
                       wedding registry machines you see in department stores).

   video and audio
   web page
   generations of
    assembler, high
   operating
    systems (Linux,
    Unix, Windows,
   utility software
   backup       and

Mike Ross BCC 2008                                                                                             Page 62
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Mike Ross BCC 2008                                       Page 63
Computer Science – Notes for Components - Stages 2 & 3

Stage 2B
Hardware components
 identification of components to address communication process functions (sending devices, communications
    devices, channels or pathways, receiving devices, messages, protocols)
 key concepts, terminology, functions, capabilities and limitations of common components in communication
     types of networks (PAN, LAN, WAN)
     factors affecting the design of networks
     digital and analogue transmissions
     network devices (network interface card, switch, router, modem, access point)
     protocols (TCP/IP, WAP, Ethernet, FTP, HTTP, SMTP)
     transmission rates (bps, Kbps, Mbps, Gbps) and the need for bandwidth
     transmission media:
        ○ copper (coaxial, twisted pair)
        ○ optical fibre (single-mode, multi-mode)
        ○ wireless (infrared, cellular, radio, microwave, satellite).
     purpose of subnets
     network standards (Ethernet standards 802.3 and 802.11, Bluetooth, IrDA, RFID).
 network topologies for LANs (star, ring, bus)
 client/server and peer-to-peer
 security of information over the internet (firewalls, authentication and encryption).

Software components
 database systems (flat file, relational)
 features and functions of web interfaces to databases
features of network operating systems (administration, resource management, security).

Stage 3A
Hardware components
 computer architecture
     role of the central processing unit (arithmetic logic unit, control unit, registers, program counter, cache),
      system clock and data bus in the fetch-execute cycle
     multi-core processor architectures e.g. dual-core, quad-core
     multi-processor and parallel system architecture
 fault diagnosis e.g. selective component removal/replacement
 hardware preventative maintenance e.g. inspection, cleaning and repair
 backup recovery systems (RAID, backup, snapshot imaging)
 virtualisation.

Software components
 purpose of operating systems
 distinguish between batch systems and real-time systems
 identify functions of operating systems (scheduling, managing concurrency, managing memory, managing
    devices, file systems)
 different programming languages (procedural, non-procedural, object-oriented, event-driven, platform-
    independent, visual, scripting).

Mike Ross BCC 2008                                                                                          Page 64