PC Data _ Components Kato4

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PC Data _ Components Kato4 Powered By Docstoc
					     Makerere University Business School
    Faculty of Computing and Mgt Science
     Department of Business Computing
                  BBC 1
 Edward Kabale
 William Ssebunya
 Ismael Kato

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         Lecture one

 PC   Fundamentals and Components

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Types of computer

    Computers can be categorized into four types

      Microcomputers
             - desktop, laptop, notebook and palmtop personal computers (PCs)
             - used in businesses, schools/colleges and homes
      Minicomputers
             - often used as multi-user systems, with 100’s of workstations or
              terminals attached to a central minicomputer, e.g. EPOS.
      Mainframe computers
             - used by large organisations which may have 1000’s of terminals, often
      Supercomputers
             - largest category of computer used mostly by scientific & industrial
               research departments, NASA, the Weather Centre, stock exchanges

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Computer Data
   PC's are data processors. PC's function is
    simple: to process data, and the
    processing is done electronically inside
    the CPU and between the other
    components. But what are data, and how
    are they processed electronically in a PC?

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Analog data
   The signals, which we send each other to
    communicate, are data. Daily data have many
    forms: sound, letters, numbers, and other
    characters (handwritten or printed), photos,
    graphics, film. All these data are in their
    nature analog,
   Which means that they are varied in their
    type. In this form, they are unusable in a PC.
    The PC can only process concise, simple
    data formats. Such data can be processed
    very effectively
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Digital data
   The PC is an electric unit. Therefore, it
    can only deal with data, which are
    associated with electricity. That is
    accomplished using electric switches,
    which are either off or on.You can
    compare with regular household switches.
    If the switch if off, the PC reads numeral
    0. If it is on, it is read as numeral 1. See
    the illustration below:

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Digital Data Cont

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Digital data cont
 The PC is filled with these switches (in
  the form of transistors). There are literally
  millions of those in the electronic
 Each represents either a 0 or a 1, so we
  can process data with millions of 0's and

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          Each 0 or 1 is called a bit. Bit is an
           abbreviation of the expression BInary digiT.
           It is called binary, since it is derived
           from the binary number system
0                        1 bit
1                       1 bit
0110                    4 bit
01101011                8 bit

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The binary number system
   The binary number system is made up of
    digits, just like our common decimal
    system (10 digit system). But, while the
    decimal system uses digits 0 through 9,
    the binary system only uses digits 0 and 1.

   See how numbers are constructed in the
    binary system, using only 0's and 1's:

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Decimal vs. Binary systems
Numbers, as known in the                Same numbers in binary
decimal-system                          system
0                                       000
1                                       001
2                                       010
3                                       011
4                                       100
5                                       101
6                                       110
7                                       111
8                                       1000

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       The most basic data processing is word
        processing. When we do word processing,
        we work at a keyboard similar to a
        typewriter. There are 101 keys, where we
        find the entire alphabet A, B, C, etc. We also
        find the digits from 0 to 9 and all the other
        characters we need:,.-;():
       All these characters must be digitized. They
        must be expressed in 0's and 1's. Bits are
        organized in groups of 8. A group of 8 bits is
        called a byte.
       8 bits = 1 byte, that is the system.
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Bytes Cont.Example
   When you write the name ―Edward", you
    write 6 letters. If the computer has to
    process that name, it will be digitized to 6
    bytes. In other words, the name Edward
    occupies 6 bytes in the PC RAM, when
    you type it, and 6 bytes on the hard disk, if
    you save it.

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   ASCII means American Standard Code for
    Information Interchange. It is an industry
    standard, which assigns letters, numbers,
    and other characters within the 256 slots
    available in the 8 bit code.

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About text and code
 Now we have seen the PC's user data,
  which are always digitized. But there are
  many different kinds of data in the PC.
 You can differentiate between 2
  fundamental types of data:
 I Program code, which are data, that
  allow the PC to function.
 II User data, like text, graphics, sound

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Program code
 An instruction is a string of data, of 0's and 1's.
  The CPU is designed to recognize these
  instructions, which
arrive together with the user input data to be

   The program code is thus a collection of
    instructions, which are executed one by one,
    when the program runs. Each time you click the
    mouse, or hit a key on the keyboard, instructions
    are sent from your software (program) to the
    CPU,telling it what to do next.
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User data
   User data are those data, which tells the
    software how to respond. The letters,
    illustrations, home pages, etc., which you
    and I produce, are created with
    appropriate software.

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   Both program code and user data are saved
    as files on the hard disk. Often, you can
    recognize the type of file by its suffix. Here are
    some examples:
   Program code START.EXE, WIN.COM, HELP.

   User data LETTER.DOC, HOUSE.BMP.

   The file name suffix determines how the PC
    will handle the file.

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The components of a computer

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Components in the system case

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Components serve specific

 ◦ BUS - connects all the components of the
   computer and provides a path from
   device/controller to the next component.
 ◦ Expansion Slots - for connecting other
   devices/controller cards to the motherboard.
 ◦ Memory Slots - provides receptacles for
   adding additional memory chips (SIMMs,
   DIMMs, or other types of memory).

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Components continued
      ◦ ZIF Socket - provides a location to insert the
        heart of the computer - the CPU.
      ◦ BIOS Chip - provides a definition of the
        system for booting.
      ◦ USB Port - some newer machines will have a
        port for the Universal Serial Bus (USB)
     Chip Set - controls most of the capabilities such
      as type of memory, I/O, etc

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Motherboards/System Board
   The Main Printed Circuit Board Inside The PC
    That Contains and Controls The Components
    That Are Responsible For Processing Data.
 Data and power infrastructure for the
  entire computer
 Manufacturers of motherboards include,
 Ait,ASUS,Foxconn,Intel,MSI,VIA,Gigabyte

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Find each of the ff
  ◦ ISA Expansion Slots (4 - long black slots at upper
  ◦ PCI Expansion Slots (4 - mid length white slots in
  ◦ Pentium II CPU Slot (long slot near right edge)
  ◦ Memory (SIMM) bank (4 white slots to right of PCI
  ◦ CPU (Microprocessor)Slot
  ◦ ROM Chip (BIOS Chip)
  ◦ Clock Oscillator
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                       Expansion Slots

   Expansion Slots - provide the ability to add extra
    components to your computer system.To get an
    idea of what they look like, check out the picture on
    next slide.
    An expansion card (also expansion board, adapter
    card or accessory card) in computing is a printed
    circuit board that can be inserted into an
    expansion slot of a computer motherboard to add
    additional functionality to a computer system.

   There are several types of expansion slots on a

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               Expansion Slots
   ISA is a PCI Expansion Slots – These are older16 bit
    expansions slots. They "talk" to the motherboard at 8 MHz
 However, these are being replaced by PCI slots. Many
  motherboard manufacturers will include one for
  older expansion cards.
 EISA - Found older Servers; slots could work with
  motherboard faster than ISA slots (32 bits at16 MHz).
  Its rare to find these on newer motherboards.
 Major drawback; often you one w’d have to run a
  "configuration utility", or program to add expansion

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           Expansion Slots

   PCI Expansion Slots are the most
    commonly found in motherboards
    today. They "talk" to the motherboard
    sending 32 or 64bits at 33 MHz.They
    offer a drastic improvement over ISA
    or EISA expansion slots.

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   ISA- Industry Standard Architecture

   EISA- Extended Industry Standard

   PCI- Peripheral Component
    Interconnect is a computer bus for
    attaching hardware devices in a computer

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Other expansion slots and cards;
 AGP- reserved for Video cards (Advanced
  Graphics Port), these are the standard graphics
  port in all new systems. They communicate to the
  motherboard at 66 MHz.
 AMR - Audio Modem Riser slot. Designed to
  allow lower cost sound and modem cards to be
  integrated into motherboards.
 CNR - Communication and Network Riser card.
  Found on i815 chipset motherboards, and is
  another attempt to lower the cost of adding both
  network as well as modem cards to a system.

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Basic Input/output System
   All motherboards include a small block of Read
    Only Memory (ROM) which is separate from
    the main system memory (RAM) used for
    loading and running software. The ROM
    contains the PC’s BIOS.

   In IBM PC Compatible computers, the
    Basic Input/Output System (BIOS),
    also known as the System BIOS, is a
    common standard defining a firmware
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   The BIOS is boot firmware, designed to be
    the first code run by a PC when powered
   Initial function: identify, test, and initialize
    system devices such as the video display
    card, hard disk, floppy disk and other
   BIOS sets the machine hardware into a
    known state, so that software stored on
    compatible media can be loaded, executed,
    and given control of the PC.
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e.g.: Phoenix BIOS

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                    CMOS RAM
   Motherboards include a separate block of memory made
    for low power consumption CMOS RAM chips, which is
    kept alive by a battery even when the PC’s power is off.

   Complementary metal–oxide–semiconductor
    (CMOS) is a technology for constructing integrated
    circuits. CMOS technology is used in
    microprocessors, microcontrollers, static RAM, and
    other digital logic circuits.

   CMOS technology is also used for a wide variety of analog
    circuits such as image sensors, data converters, and highly
    integrated transceivers for many types of communication.

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Motherboard Determines
   CPU type and speed
   Chipset
   Secondary cache type
   Types/number of slots
   Type of memory
   Number of memory sockets and maximum
   Type of case
   ROM
   Plug & Play compatibility
   Type of keyboard

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Motherboard cont
 Holds The Processor
 Memory
 Expansion Slots
 Connects Directly or Indirectly to Every Part of
  The PC
   Various Interconnections or Buses

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Form Factors
 Form factor means the size and shape of
  the actual motherboard
 4 most common Form Factor
    ◦   Baby AT
    ◦   ATX & microATX
    ◦   Slim line NLX(New Low Profile Extended)
    ◦   BTX

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             Form Factors: AT
   AT; Short for Advanced Technology, the
    AT is an IBM PC model introduced in 1984.
   Most motherboards were benchmarked on
   At a size of 13.5" X 12", this form factor
    soon became another standard followed by
    other manufacturers.
   Other things about it that were copied;
    screw placement, expansion slot positioning,
    and component placement

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Drawbacks of AT
   AT required a lot of space in the
    computer case

   The physical size of the board, which
    is 12" wide, often caused the board to
    overlap with space required for the
    drive bays

   It was replaced by Baby AT
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                Baby AT
 The AT board was replaced with a 'baby
  AT' or 'mini AT' board as tech. advanced.
 Expansion slots and the screw positioning
  of AT reduced to 13" X 8.5 or 9" board.
 Baby AT became popular and was
  designed for peripheral devices —
  keyboard, mouse, and video — to be
  contained on circuit boards that were
  connected by way of expansion slots on
  the motherboard
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Baby AT: Problems
   As processors became larger, the Baby AT
    form factor did not allow for space to use
    a combination of processor, heat sink, and
    fan. The ATX form factor was then
    designed to overcome these issues.

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 Came with the need for a more
  integrated form factor
 ATX defined standard locations for the
  keyboard, mouse, I/O, and video
 Expansion slots were put onto separate
  riser cards that plugged into the
  motherboard, thus overall size of the
  computer and its case was reduced.
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    Other ATX improvements
 A single 20-pin connector for the power supply
 A power supply to blow air into the case instead
  of out for better air flow;
 Less overlap btn motherboard & drive bays;
 Integrated I/O Port connectors soldered directly
  onto the motherboard.
 Allows for better component access;
 In some ways is faster and more stable;
 Smaller board- approx. 9.5" X 12" to 8.5 X 11.12
 An overall better design for upgrading.
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microATX: Feature Summary

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Low Profile Extended- LPX

   Found in low-profile cases (desktop model
    as opposed to a tower or mini-tower)
   Have sound & video integrated onto
   Have riser card arrangement for expansion
    cards where expansion boards run parallel
    to motherboard.
   Low-cost and space saving products
   BUT: are difficult to repair coz of space &
    overall non-standardization

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Slim line NLX (New Low Profile Extended)

 ―Updated  LPX" form factor
 Offered support for larger memory
  modules, tower cases, AGP video
  support and reduced cable length.
 Motherboards are easier to remove.
 More component options for
  upgrading and repair.

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 The Balanced Technology Extended form
 A total break away from the popular and
  dominating ATX. Non-evolutional
 Developed to take advantage of technologies
  such as Serial ATA, USB 2.0, and PCI Express.
 Changes include;
    • Better component placement for back panel I/O
    • Smaller than microATX systems.
    • Increased number of system slots.

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BTX: Other adv.
 Uses in-line airflow;
 Memory slots and expansion slots have
  switched places, thus main components
  (processor, chipset, and graphics
  controller) use same airflow;
 Reduced the number of fans needed in
  the system;
 Reduced noise. BUT: ATX remains
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Motherboards sizes

    ◦ Standard AT = 12" w x 13.8" long

    ◦ Baby AT = 8.57" w x 13.04" long

    ◦ LPX = 9.0" w x 13.0 long

    ◦ ATX = 9.6" w x 12.00 long

   NB. Sizes are important if you are replacing an
    existing motherboard
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Motherboard Interface
   Small Computer System Interface.
    An interface, usually on a separate card,
    that allows you to interface with up to 7
    individual devices such as hard and floppy
    drives, tape drives, CD-ROM drives, etc.
    Has transfer rates of up to 32MBPS, but
    operate normally at a much slower rates.
    Has its own built-in control circuitry.

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Connectors Cont
 Peripheral Component
  Interconnect. It is an Intel developed
  high-speed system bus supporting
  32-bit or 64-bit data paths.
  Sometimes used to reference the
  slot or the type of connections on a
  interface card

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Connectors Cont
 EIDE - Enhanced Integrated Drive
 PCI - Peripheral Component Interface –
  Expansion slot
 VGA - Video Graphics Array -Graphics
 IDE-Intelligent Drive Electronics. A term that
  describes a hard disk drive interface that
  combines features of other interfaces and
  has additional features. IDE devices have
  their own control circuitry; however, an IDE
  interface supports only devices.

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                     PC Buses
   The PC's bus is the circuitry that ties all
    the devices on your motherboard together.

   To understand a PC's bus, you must be aware
    that a computer has many components such as a
    Central Processing Unit , clocks, storage devices,
    input/output devices, etc.

   These devices must be linked together to
    perform a function. The 'bus' provides a highway
    for passing information between the devices on
    the system.
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Internal and External Bus
   The Internal Bus connects different
    components inside the case: CPU, system
    memory, and all other components on the
    motherboard. also referred to as the
    System Bus.
   The External Bus connects the different
    external devices, peripherals, expansion slots,
    I/O ports and drive connections to the rest
    of the computer.
   External Bus allows expansion of
    computer's capabilities, i.e.; Expansion Bus.
    Generally slower than system bus.
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Types of Buses
  CPU bus or 'system' bus.
 The system bus connects the CPU with RAM
  and maybe a buffer memory (L2-cache). The
  system bus is the central bus. Other busses
  branch off from it.
  ◦ Address bus
  ◦ Memory bus

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Data Bus
 Data has to be exchanged between
 Some of the dedicated electronic
  pathways or wires of the Internal Bus or
  the External Bus that move data.

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Address Bus/ Memory Bus

 Information used to describe the memory
  locations travels along the address bus.
 Size or width of address bus directly
  corresponds to number of address locations
  that can be accessed.
 E.g A 286 CPU with a 16 bit address bus can
  access over 16 million locations, or 16 Mb of
 A 386 CPU with a 32 bit address bus can
  access up to 4 GB of RAM.

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I/O or Expansion Bus
 The I/O busses move data. They connect
 all I/O devices with the CPU and RAM.
 I/O devices are those components, which
 can receive or send data (disk drives,
 monitor, keyboard, etc. ). In a modern
 Pentium driven PC,
 There are two or three different I/O

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Three different I/O busses
   The ISA bus, which is oldest, simplest, and
    slowest bus.

   The PCI bus, which is the fastest and
    most powerful bus.

   The USB bus, which is the newest bus. It
    may in the long run replace the ISA bus.

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Bus Standards/Types
   There are several "bus" standards, among
    them are:

    ◦ Industry Standard Architecture (ISA).
    ◦ Micro Channel Architecture (MCA)
    ◦ Enhanced Industry Standard
      Architecture (EISA)
    ◦ Peripheral Component Interface (PCI)
    ◦ VESA Bus
    ◦ Universal Serial Bus

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Central Processing Unit(CPU)
   Is a complete computation engine that is
    fabricated on a single chip made up of a
    semiconductor Silicon

   CPU executes program instruction codes,
    perform mathematical & logical calculations,
    and controls Input/output functions

   They operate at ultra-fast speeds – doing
    over a billion operations very second

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The computer’s brain
  CPU: Detail
CPU: Picture results
Processor Speed
 The speed is measured in Megahertz or MHz
 1 MHz = 1 million cycles per second (or computer
 If a processor runs @ 2000 MHz, then the computer
  runs @ 2000,000,000 cycles per sec,
 Which in more basic terms is the amount of
  instructions your computer can carry out.
 1 Gigahertz or GHz = 1000 MHz
 1000 MHz (Megahertz) = 1GHz (Gigahertz)
 and 1GHz = 1000,000,000 Cycles per second
  (or computer instructions)
Processor Types
   Single cores run a single processor at a time
   Dual cores run 2 processors at a time
   Triple core
   Quad core/ Core 2 Duo have four
    processors embedded in them;
   Intel Celeron; a lower budget Intel processor
   The more processors, the higher the
CPU Cache
 Stores memory data and speeds up
  operation by making recently accessed
  data immediately available to the
 The larger the L2 cache, the bigger the
  performance increase on a computer
 Some Intel CPUs utilize one larger shared
        Front-side bus (FSB)
   FSB is rate at which an Intel processor communicates
    with the motherboard's memory controller.
   High FSB speed boosts performance of RAM-intensive
   Thus reducing the time it takes for data to move
    between the CPU and the memory controller.
   The upper limit of FSB speeds today on Intel's highest-
    end Core 2 Extreme processors is 1,600MHz, while
   Older processors have FSB speeds of 800MHz,
    1,066MHz, or 1,333MHz.
   It’s gd for motherboards 2 supports FSB speed of
    processor one wants 2 buy, however, 2 avoid
    performance probs.
CPU Structure
CPU Producers
 Intel for Pentium and Core CPU
 AMD(Advanced Micro Devices)-It uses
  the Intel instruction set.

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CPU Types, evolution
Time        Intel                                           AMD
1978-1989   1st-3rd Generation
1989-1993   4th Generation                                  AMD486
1993-1997   5th Generation(Pentium)                         K5
1996-1999   6th Generation(Pentium Pro,Pentuim              K6,K6-2,K6-3,K7
            II,Pentium III,Celeron)                         (Athlon,Duron)
2000-2005   7th Generation (NetBurst,Pentium                Athlon XP,Athlon
            4,Pentium D,Celeron)                            MP,Athlon XP-M
2003        Pentium M (Centrino)                            K8 (Athlon 64x2,Turion
                                                            64,Turion 64x2)
2006        8th Generation (Core, Core 2)
            Quad and Octo core ??

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How CPUs work?

A microprocessor -- also known as a CPU
or central processing unit -- is a complete
computation engine that is fabricated on a
               single chip.
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• Using its ALU (Arithmetic/Logic Unit), a
microprocessor can perform mathematical operations
like addition, subtraction, multiplication and division.
•Modern microprocessors contain complete floating
point processors that can perform extremely
sophisticated operations on large floating point
• A microprocessor can move data from one memory
location to another.
• A microprocessor can make decisions and jump to                   a
new set of instructions based on those decisions.

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Main parts of a CPU
 ◦ Arithmetic unit (AU) is made up of
 Arithmetic Logic Unit (ALU) – arithmetic
  calculations + logic operations
 Accumulators (ACC) – where arithmetic
  calculations are made
 Condition Code Register (CCR) – set based
  on results of ALU; 4 common bits: Zero,
  Negative, Overflow, Carry

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Control Unit (CU)
   Control unit made up of:
    ◦ Memory Address Register (MAR) – holds current
      address where Processor is accessing
    ◦ Memory Data Register (MDR) – holds instruction
    ◦ Instruction Register (IR) – holds fetched
      instruction  decoder circuitry
    ◦ Program Counter (PC) – holds next instruction
    ◦ Control Logic (CL) – synchronisation

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Processor Terminology
 CPU registers -hold data before and after
  processing in the ALU
 The bit size of the Information that can
  be held and processed by the General
  Purpose registers.
 ALU also determines the processing
  capability of the CPU.
 The register size determines software
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   CPU packaging refers to the way the CPU
    can be installed on the motherboard.
   In most cases the CPU is installed into a Pin
    Grid Array (PGA) socket.
   The main problem with this arrangement is
    that the pins on the CPU chip are very easy
    to damage during insertion and removal.
   Intel have also introduced a Land Grid Array
    (LGA) form factor in which the pins are
    located on the board.

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Instruction Set
 In order to make a CPU perform tasks, it
  must be given instructions by a software
  program. The instructions that a CPU can
  process are referred to as its instruction set.
The instruction set for a typical computer are;
 Data Transfer
 Arithmetic Operations
 Logical Operations
 Test and Branch Instructions

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System Clock speed
   Controls the timing of every action
    performed by the CPU.

   The faster the speed of the system clock,
    the greater the performance obtained
    from the PC.

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Over clocking
 A new chip clock speed is set at optimum
  based on systems testing.
 Over clocking increases the clock speed,
  improving performance of the CPU
 This is done using the CMOS setup by
  adjusting the CPU speed or Advanced
  Chipset features properties.
 Increasing the clock speed requires more
  power and sufficient cooling because it
  generates more heat.
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Word Size
   The number of bits that the CPU can
    process simultaneously. Normally groups
    of 8, 16, 32, 64, 128 bit words are
    processed as a unit during input, output
    and logic instructions.

   Word size is a major factor in
    determining the speed of a processor.

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Bus Size
   Buses are the lines along which data is
    transmitted. This data can be in the form
    of data and instructions as well the
    addresses of the data and the

   The width of a data bus determines how
    many bits can be transmitted
    simultaneously and the maximum address
    which can be referenced.
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   An address bus (that may be 8, 16 or 32 bits wide) that
    sends an address to memory

   A data bus (that may be 8, 16 or 32 bits wide) that can
    send data to memory or receive data from memory

   An RD (read) and WR (write) line to tell the memory
    whether it wants to set or get the addressed location

   A clock line that lets a clock pulse sequence the

   A reset line that resets the program counter to zero (or
    whatever) and restarts execution

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                    PC Memory
Primary storage or memory: Is where the data and
 program that are currently in operation or being
 accessed are stored during use.

   Instructions and data are held in main memory, which is
    divided into millions of individually-addressable storage units
    called bytes.

   One byte can hold one character, or it can be used to hold a
    code representing, for example, a tiny part of a picture, a
    sound, or part of a computer program instruction.

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                       PC Memory
   The total number of bytes in main memory is referred to as the computer’s
    memory size. Computer memory sizes are measured as follows:
   1 Kilobyte (Kb)                 =       1000 bytes
    1 Megabyte (Mb)        =        1,000,000 (1 million) bytes
    1 Gigabyte (Gb)        =        1,000,000,000 (1 billion) bytes
    1 Terabyte (Tb)                 =       1,000,000,000,000 (1 trillion)
  1000 bytes form          =        1 Kilobyte
 1000 kilobytes           =        1 Megabyte(MB)
 1000 MB                  =        1 Gigabyte(GB)
 1000 GB                  =         1 Terabyte(TB)

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Main memory consists of a
number of storage locations,
each of which is identified by
a unique address

 The ability of the CPU to
 identify each location is
 known as its

  Each location stores a word
  i.e. the number of bits that
  can be processed by the
  CPU in a single operation.
  Word length may be
  typically 16, 24, 32 etc
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Types of main memory

There are two types of main memory, Random Access Memory (RAM) and Read
Only Memory (ROM)

Random Access Memory (RAM)
holds its data as long as the computer is switched on

All data in RAM is lost when the computer is switched off

Described as being volatile(It depends on constant supply of power)

It is direct access as it can be both written to or read from in any order

 Its purpose is to temporarily hold programs and data for processing. In
 modern computers it also holds the operating system
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    Types of RAM
1.   Dynamic Random Access Memory (DRAM)
•   Its used as the main or system memory of a PC.It
    stores the OS,applications and data while they
    are running.
•   Contents are constantly refreshed 1000 times per
•   Access time 60 – 70 nanoseconds

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Types of RAM Cont
2.Synchronous DRAM (SDRAM)
It was designed to run at the motherboard clock
   speed, was introduced alongside Pentium CPU
   based systems.
Quicker than DRAM
3.Rambus (RDRAM)
• New    type of RAM architecture
• Access   time 20 times faster than DRAM
• More   expensive
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     Types of RAM Cont

 Double Data Rate SDRAM (DDR SDRAM)
-Is a variant of SDRAM where data is
  transferred twice in one cycle.
 DDR2 Is the new generation of DDR
  SDRAM,offering the potential for improved
 It also uses a lower voltage resulting in power
 Find out SRAM(Research)??
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   Static Random Access Memory (SRAM) is a
    type of semiconductor memory;
   Static indicates that it does not need to be
    periodically refreshed;
   Uses bistable latching circuitry (duo state IC) to
    store each bit of data.
   SRAM exhibits data remanence, but is still volatile
    in the conventional sense that data is eventually
    lost when the memory is not powered.
   The term SDRAM, which stands for synchronous
    DRAM, should not be confused with SRAM.

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Data remanence
 Residual representation of data that has
  been deleted.
 Data is involuntarily recovered by the
  storage media.
 May lead to disclosure of sensitive
  information to third party

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RAM Note
      Motherboards are designed to support
       specific types of RAM.

      You should always check which types of
       memory can be fitted before supplying or
       installing upgrades.

      The memory must be equal to or faster
       than the motherboard clock speed.
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Read Only Memory (ROM)

   Non-volatile, with contents permanently etched
    into the memory chip at the manufacturing stage

   Used for example to hold the bootstrap loader, the
    program which runs as soon as the computer is
    switched on and instructs it to load the operating
    system from disk into memory.

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           ROM Types
 1.Programmable read-only memory,(PROM) A
  memory chip on which data can be written only
 Once a program has been written onto a
  PROM, it remains there forever. Unlike RAM,
  PROMs retain their contents when the
  computer is turned off..

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   To write data onto a PROM chip, you need a
    special device called a PROM programmer or PROM
    burner.The process of programming a PROM is
    sometimes called burning the PROM.

   2.An EPROM (Erasable programmable read-only
    memory) is a special type of PROM that can be
    erased by exposing it to ultraviolet light. Once it
    is erased, it can be reprogrammed. An EPROM is
    similar to a PROM, but requires only electricity to
    be erased.

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Cache Memory
      Very fast memory used to improve the speed of a
       computer, doubling it in some cases
      Acts as an intermediate store between the CPU and
       main memory
      Stores the most frequently or recently used instructions
       and data for rapid retrieval
      Generally between 1Kb and 512Kb
      Much more expensive than normal RAM

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Memory Cache speeds up a computer by storing data
the computer has recently used. There are 2 types :
               Internal & External

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External Cache
If the computer cannot find
what it needs in the Internal
Cache, it looks in the external
cache. This is usually located on
the Motherboard. In some CPU
chips the External cache is built

                                                   Internal Cache
                                                   When the computer needs
                                                   data it first looks in the
                                                   Internal cache. This is
                                                   located on the CPU chip and
                                                   provides the fastest way for
                                                   the computer to get data.
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Virtual memory

                  Space on a hard disk used to
                  temporarily store data and
                  swap it in and out of RAM
                  as needed.

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                        Memory Characteristics

   A given motherboard will only be able to fit SDRAM,RDRAM,DDRRAD or
    DDR2 RAM (not a mixture). In addition ,there can be compatibility issues
    even if the memory is of the correct type.
   Memory Speed. Before fitting any new RAM, you must check the correct
    speed at which the motherboard operates
   Memory Banks. When memory is installed, It must fill a bank. When a
    processor fetches data from memory, it fetches a bank. the size of the bank
    varies according to the processor type.Currently,most motherboards
    support a 64-bit data bus and typically 1 slot represents 1 bank.
   Chips. The capacity of a memory module is determined by the number of
    chips and the size of each chip (Each chip typically has a size of 64MB or
    32 MB)

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       Memory Characteristics Cont
   Single sided memory. Single sided memory
    is a module that fills a single bank(that is the
    computer can access all of the memory on
    the module at the same time)Single-sided
    memory has 8 chips

   Double-sided(or dual-bank)memory has two
    banks, the computer can access one bank or
    the other but not both simultaneously.
    Double-sided has 16 chips

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Memory Packaging
 DIMM(Dual In-Line Memory Modules) are
  used for most memory types, but DIMM
  modules and connectors are not
 SDRAM-168 pins and two notches
 DDR SDRAM -184 pins and one notch
 DDR2SDRAM-240 pins and one
  notch(keyed differently to DDR SDRAM
 RIMMs for Rambus Inline Memory Module

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             Storage devices
 Storage devices use either magnetic or optical
  technology to store data.
 Capacities of storage devices range from 1.44MB
  for a standard 3.5 floppy disk to multiple
 The main storage device in a computer is one or
  more fixed hard drives.
 Other storage devices (such as a floppy
  drive,CD,DVD drive or tape drive) are used to
  transfer information to and from the
  Computer.(Removable storage)

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Storage devices are typically internal
   In case of removable storage devices, the drive
    is positioned at the front of the case so that
    media can be inserted and removed.

   External Storage devices are increasingly
    popular for backup and data transfer as they
    offer more capacity than traditional removable
    storage disks.E.g External hard drive would
    typically be connected to the computer via a
    USB or fire wire port.
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                  Hard Drives
   Even with the advances in the speed and
    capacity of other types of storage technology,
    the Hard Disk Drive(HDD) still remains
    the primary method of storage for PC
    data.(OS files, application files, user data
    system software files(such as drivers)

   On a server PC,the hard disks will store
    individual user files and shared sources of
    information, such as databases.
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   The original hard disk drives stored as
    little as 10 MB-the same as about 7 floppy
    disks-but advances in hard disk
    technology have enabled disks of over
    200 GB to be created-the same as about
    142,000 floppy disks.

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            Hard Disk Structure.
   HD Consists of one or more Platters of metal or
    glass held in a sealed unit.
   The platters revolve around a spindle and the
    read/write heads for each surface are fixed to a
    single arm called the Head actuator
   Each platter has two usable sides, marked in
    concentric circles called tracks.
   The tracks are divided into a number of segments
    called sectors, each holding 512 bytes of data.
   A collection of tracks, immediately above and
    beneath one another is called a Cylinder.

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A disk storage system

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          Hard Disk Performance
   The Performance of a hard disk is a measure of
    how fast it can read and write data. A number of
    indicators are used to measure performance .
   1.The speed at which the disks can
    spin(measured in Revolutions per Minute
    [RPM])The faster the RPM,the faster the drive
   2.The Internal Transfer rate(or data or disk
    transfer rate) of a drive is a measure of how fast
    read/write operations are performed on the disk

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Internal Transfer Rate
   The internal transfer rate(transfer
    rate)measures how fast data can be
    transferred to the CPU across the bus.
   The amount of cache memory can help to
    sustain better transfer rates. A high
    performance disk may feature a 4MB or
    better cache.
   Burst transfer rate. This is the maximum
    possible transfer rate under ideal conditions
    and cannot be sustained over a long period

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