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Why Its Important to Know What’s Inside Your PC
If you want to take advantage of ever-advancing PC technology, get the most for your PC dollar, and
allow your PC to grow with your capabilities, you need to know what’s inside your PC. You need to
know because personal computing is very personal. You are the decision maker. A little knowledge
about what’s inside can save you big bucks and make you a more effective user.
Inside the Case
There are only a few major components in a computer such as the motherboard, plug-in boards,
memory, disk drives and the power supply.
Once the cover is removed, you will see several boards that are plugged on the large motherboard that
sits on the floor of the chassis. The motherboard is the main circuit board in the computer to which the
microprocessor, memory, power supply, and other devices are connected.
The bus is a pathway used to send data (input and output) between components inside the computer.
Empty expansion slots on the motherboard inside most computers allow you to plug in adapter cards.
These cards contain electronic components that upgrade or expand the computer’s capabilities. For
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example, you can easily add a fax or modem to a system that doesn’t have one. Popular expansion
boards include video card (enables interfacing with video monitors), sound card (enables sounds to be
captured and stored on disk, also enables sounds to be played through external speakers), modem card
(permits communication with remote computers via a telephone link), network interface card (enables
the exchange of data between microcomputers in a PC network).
Sockets or ports mounted on the outside of the computer are used to connect peripherals such as
keyboard, mouse and printer to the computer. External peripheral devices can be linked to the computer
via cables through either a serial port or a parallel port. However, as input/output demands have
increased, serial and parallel ports have become bottlenecks to system performance.
Universal Serial Bus (USB) Port
Anyone who has been around computers for more than two or three years knows the problem that the
Universal Serial Bus is trying to solve -- in the past, connecting devices to computers has been a real
Printers connected to parallel printer ports, and most computers only came with one. Things like
Zip drives, which need a high-speed connection into the computer, would use the parallel port as
well, often with limited success and not much speed.
Modems and mice used the serial port, but so did some printers and a variety of odd things like
digital cameras. Most computers have at most two serial ports, and they are very slow in most
Devices that needed faster connections came with their own cards, which had to fit in a card slot
inside the computer's case. Unfortunately, the number of card slots is limited and you needed a
Ph.D. to install the software for some of the cards.
The goal of USB is to end all of these headaches. The Universal Serial Bus gives you a single,
standardized, easy-to-use way to connect up to 127 peripheral devices to a computer.
Just about any computer that you buy today comes with one or more Universal Serial Bus connectors on
the front or the back. These USB connectors let you attach everything from mice to printers to your
computer quickly and easily. The operating system supports USB as well (Plug and Play), so the
installation of the device drivers is quick and easy, too. Compared to other ways of connecting devices
to your computer (including parallel ports, serial ports and special cards that you install inside the
computer's case), USB devices are incredibly simple to connect!
Just about every peripheral made now comes in a USB version. A sample list of USB devices that you
can buy today includes Printers, Scanners, Mice, Joysticks, Digital cameras, Memory sticks, Web cams,
Speakers and many others.
Connecting a USB device to a computer is simple -- you find the USB connector on the front or back of
your machine (these days computer manufacturers like Dell are placing the USB connectors on the front
of the computer for convenience) and plug the USB connector into it.
Most computers that you buy today come with two USB sockets. With so many USB devices on the
market today, you easily run out of sockets very quickly. For example, if you wanted to simultaneously
use a USB printer, a USB scanner, and a USB Web cam on a computer that has only 2 USB ports, the
obvious question is, "How do you hook up all the devices?"
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The easy solution to the problem is to buy an
inexpensive USB hub. You plug the hub into your
computer, and then plug your devices (or other hubs)
into the hub. By chaining hubs together, you can
build up dozens of available USB ports on a single
The central processing unit, or CPU for short,
controls all of the computer’s functions, makes all
calculations, and processes all data that you enter.
Internal memory, or RAM, stores the programs you are using (such as Windows, Excel etc) and the data
you are processing (such as a letter or a database).
Storage devices such as floppy drives, CD drives and hard drives are used to store programs and data.
The power supply provides the required dc voltage required for the computer. It converts the 110V or
220V ac from your local power company to the 9-12V dc required. It also has a cooling fan in it that
sucks air in from the front of the computer and forces it out through the grill in the back of the power
Your processor is the brain of your computer. It is also referred to as the microprocessor or central
processing unit (CPU). It interprets all the instructions that it receives from various devices and then
executes those instructions, such as telling your printer to print. The faster the processor, generally the
faster the computer will be able to perform those instructions and tasks. In terms of computing power,
the CPU is the most important element of a computer system.
A microprocessor is fabricated on a single chip of silicon. A chip might be as large as an inch on a side
and can contain tens of millions of transistors. The first microprocessor was the Intel 4004, introduced in
1971. The 4004 was not very powerful -- all it could do was add and subtract, and it could only do that 4
bits at a time. But it was amazing that everything was on one chip. Prior to the 4004, engineers built
computers either from collections of chips or from discrete components (transistors wired one at a time).
The 4004 powered one of the first portable electronic calculators.
The first microprocessor to make it into a home computer was the
Intel 8080, a complete 8-bit computer on one chip, introduced in
1974. The first microprocessor to make a real splash in the market
was the Intel 8088, introduced in 1979 and incorporated into the IBM
PC (which first appeared around 1982). If you are familiar with the PC market
and its history, you know that the PC market moved from the 8088 to the 80286
to the 80386 to the 80486 to the Pentium to the Pentium II to the Pentium III to
the Pentium 4. All of these microprocessors are made by Intel and all of them Intel 8080
are improvements on the basic design of the 8088. The Pentium 4 can execute
any piece of code that ran on the original 8088, but it does it about 5,000 times faster!
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The most successful family of microprocessors is Intel’s. However, other microprocessor families are
manufactured by Apple, Sun, Motorola, Digital and others. Over the years, the
chips in each family have become more and more powerful. Programs written for
an Intel chip did not normally run on a Motorola chip; and programs that ran on an
IBM computer (using an Intel microprocessor) did not normally run on an Apple
computer (using a Motorola microprocessor), and vice versa.
But this is all changing. As of 2006, Intel and Apple have joined forces to manufacture Macs using the
Intel microprocessor. Now every new Mac uses a chip based on Intel’s new dual core technology. This
also means that soon, software developed for IBM Pcs and clones can also be used on Macs. A dual
core processor is like having two CPUs on a single chip. It can therefore take more data and process
more data at a much faster rate. Dual-core processors deliver a quantum leap in processing capacity
without a comparable increase in power consumption.
Chip-makers AMD and Intel have released dual core processors aimed at users who need high
arithmetic performance and use mainly multithreaded applications. So-called 'multithreaded
applications' benefit from an additional CPU core because subroutines can be allocated to different
arithmetic and logic units. Programs such as CAD/CAM, gaming, and audio or video processing benefit
particularly from a second processor core. With the power of dual cores, or computing engines, the
processors can manage numerous tasks faster in a more energy-efficient manner.
Relatively little multithreaded software is used on standard office and home computers, so the purchase
of a high-end dual core processor is rarely justified. However, mainstream users can still benefit
from dual core technology. If several applications are active at the same time and certain tasks are
stalled, then a dual core chip is worth having. For example, a hard disk defragmenter may be running in
the background, leaving insufficient resources for a foreground application like a presentation. They also
can operate more smoothly when multiple applications are running, such as writing e-mails while
downloading music or videos and conducting an anti-virus scan or anti-spyware scan. In these
circumstances, a dual core chip can be very helpful even on a standard office PC.
In July of 2006, Intel introduced its new line of dual processors – the core 2 duo processor for desktops,
and the core 2 Extreme processor for laptops and workstations.
The success of the Intel line of microprocessors led other firms such as AMD (Advanced Micro
Devices) and Cyrix to duplicate, or clone them. The AMD Duron, AMD Athlon, AMD Sempron and
AMD K6 line of microprocessors are very popular. AMD’s dual core processor is the Athlon 64.
When you see ads or read articles about computers, you’ll encounter phrases such as “It has a fast 2.6
GHz, 64-bit Intel Pentium 4 processor”. These buzz-words all have meanings that indicate to some
extent the speed and power of a microprocessor.
Wider highways can carry more and faster traffic than narrower ones. The same is true of computers;
the wider the bus, the more data they can carry and process, the faster and more powerful they are. The
bus is like the highway, and the bits are like the traffic on the highway. The term ‘word size’ is used to
describe the number of bits that the CPU can access from RAM simultaneously. For example, a 16-bit
CPU can process 16 bits at a time, and a 64-bit CPU can process 64 bits at a time.
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All microprocessors have a built-in system clock that sets the pace for all microprocessor operations.
This clock speed is specified in Megahertz (MHz – millions of cycles per second) or Gigahertz (GHz-
billions of cycles per second). In many cases, the higher the clock rate, the faster the computer. A
computer’s processing speed today is specified in terms or MHz or GHz.
So, a 64-bit, 2.6GHz microprocessor can process 64 bits at a time 2.6 billion times per second! Today’s
dual core processors have processing speeds in excess of 3 GHz.
Random Access Memory (RAM)
Random Access Memory (RAM) is the workhorse behind the performance of your computer. RAM
temporarily stores information from your operating system, applications, and data in current use. The
access speed of RAM is much faster as compared to that of secondary storage devices such as the hard
drive or the CD drive. This gives your processor fast access to the critical information that makes your
programs run. The amount of RAM you have determines how many programs can be executed at one
time and how much data can be readily available to a program. It also determines how quickly your
applications perform and how many applications you can easily toggle between at one time. Simply put,
the more RAM you have, better the speed of your computer, and the more programs you can run
smoothly and simultaneously.
RAM is considered volatile storage because the contents of RAM are lost when the power is turned off.
RAM is called "random access" because earlier read-write memories were sequential and did not allow
How the CPU and Memory Work Together
The CPU and memory work together to run programs and process data. The CPU has two main
the control unit, and
the arithmetic and logic unit (ALU)
During program execution, the first in a sequence of program instructions is moved from RAM to the
control unit, where it is decoded and interpreted. The control unit then directs other processor
components to carry out the operations necessary to execute the instruction.
The arithmetic logic unit (ALU) performs all arithmetic computations (addition, subtraction,
multiplication, division) and all logic operations (comparisons to determine how one value compares to
another – for eg., it can determine if one value is equal to, greater than, or less than another value).
These two units – the control unit and the ALU work together with memory in a 4-step process to
complete a single cycle, called the machine cycle. The machine cycle has 4 steps:
1. FETCH: The control unit fetches the next instruction stored in memory and stores in a small
memory area in the control unit called a register
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2. DECODE: The control unit interprets (decodes) the instruction and moves the data it refers to
from memory to the ALU
3. EXECUTE: The ALU performs any required arithmetic or logic operations on the data
4. STORE: The results of the arithmetic or logic operations are stored in primary memory, or
temporarily in a register in the ALU called an accumulator.
How Bits and Bytes Work
If you have used a computer for more than five minutes, then you have heard the words bits and bytes
(not bites). Both RAM and disk capacities are measured in bytes, as are file sizes.
You might hear an advertisement that says, "This computer has a 32-bit Pentium processor with 128
megabytes of RAM and 40 gigabytes of hard disk space." In this section, we will discuss bits and bytes.
The Binary Number System
We work with decimal digits every day. Computers happen to operate using the base-2 number system,
also known as the binary number system (just like our base-10 number system is known as the decimal
number system). The reason computers use the base-2 system is because it makes it a lot easier to
implement them with current electronic technology. You could wire up and build computers that operate
in base-10, but they would be fiendishly expensive right now. On the other hand, base-2 computers are
So computers use binary numbers, and therefore use binary digits in place of decimal digits. The word
bit is a shortening of the words "Binary digIT." Whereas decimal digits have 10 possible values ranging
from 0 to 9, bits have only two possible values: 0 and 1. Therefore, a binary number is composed of only
0s and 1s, like this: 1011. Starting at zero and going through 10, counting in decimal and binary looks
0= 0 6= 110
1= 1 7= 111
2= 10 8=1000
3= 11 9=1001
4= 100 10=1010
Bits are rarely seen alone in computers. They are almost always bundled together into 8-bit collections,
and these collections are called bytes. Why are there 8 bits in a byte? A similar question is, "Why are
there 12 eggs in a dozen?" The 8-bit byte is something that people settled on through trial and error over
the past 50 years.
When you type in characters on your computer keyboard, the binary number assigned to each character
depends on the code being used. The computer industry uses several encoding schemes, the most
important of which are the following:
ASCII (pronounced “as-key”) is the code most often used on microcomputers. In the ASCII
character set, each character on your keyboard is given a specific binary value between 0 and 127.
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Computers store text documents, both on disk and in memory, using these codes.
Bytes are frequently used to hold individual characters in a text document. One byte can store a
character such as A, b, = , !, ? or %. For example, if you use Notepad in Windows to create a text
file containing the words, "Information Technology" Notepad would use 1 byte of memory per
character (including 1 byte for the space character between the words). When Notepad stores the
sentence in a file on disk, the file will also contain 1 byte per character and per space.
Try this experiment: Open up a new file in Notepad and insert the sentence, "Information Technology"
in it. Save the file to disk under the name size.txt. Close the file, right click on its icon, click Properties,
and look at the size of the file. You will find that the file has a size of 22 bytes on disk: 1 byte for each
character. If you add another word to the end of the sentence and re-save it, the file size will jump to the
appropriate number of bytes.
If you were to look at the file as a computer looks at it, you would find that each byte contains not a
letter but a number -- the number is the ASCII code corresponding to the character (see below). So on
disk, the numbers for the file look like this:
I n f o r m a t i o n T e c h n o l o g y
73 110 102 111 114 109 97 116 105 111 110 32 84 101 99 104 110 111 108 111 103 121
Note the use of 32 for a space -- 32 is the ASCII code for a space. We could expand these decimal
numbers out to binary numbers (so 32 = 00100000) if we wanted to be technically correct -- that is how
the computer really deals with things.
EBCDIC (pronounced “eb-see-dick”) is the code used most often on mainframe computers.
ASCII and EBCDIC may be alright for English, but what if you wanted to work with French, Arabic
or Chinese that contain a large number of characters in their alphabet? Unicode is a 16-bit code that
can handle a large number of characters. So programs using UNICODE, such as Windows XP, can
support the processing and display of a number of different languages.
Lots of Bytes
When you start talking about lots of bytes, you get into prefixes like kilo, mega and giga, as in kilobyte,
megabyte and gigabyte (also shortened to KB, MB and GB). The following table shows the approximate
Exact Size Approximate Size
kilobyte 1,024 1,000 KB
megabyte 1,048,576 1,000,000 MB
gigabyte 1,073,741,824 1,000,000,000 GB
terabyte 1,099,511,627,776 1,000,000,000,000 TB
You can see in this chart that kilo is about a thousand, mega is about a million, giga is about a billion,
and so on. So when someone says, "This computer has a 2 gig hard drive," what he or she means is that
the hard drive stores 2 gigabytes, or approximately 2 billion bytes, or exactly 2,147,483,648 bytes. How
could you possibly need 2 gigabytes of space? When you consider that one CD holds 650 megabytes,
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you can see that just three CDs worth of data will fill the whole thing! Terabyte databases are fairly
common these days, and there are probably a few petabyte databases floating around too.
How Much Do You Need?
It's said that you can never have enough money, and the same seems to hold true for RAM, especially if
you do a lot of graphics-intensive work or gaming. Next to the CPU itself, RAM is the most important
factor in computer performance. If you don't have enough, adding RAM can make more of a difference
than getting a new CPU!
Today’s personal computers typically feature between 256 MB and 2 GB of RAM. The amount of
RAM your computer needs depends on the software you use. RAM requirements are normally specified
on the outside of a software package. Most of today’s computers use a type of RAM called SDRAM
(synchronous dynamic RAM). SDRAM is fast and relatively
inexpensive. Recent innovations such as double data rate (DDR)
have increased SDRAM speed. These memory chips are called
DDR-SDRAM. Memory is available for purchase on a small
circuit board called a memory module. The type of memory
module used in today’s computers is the DIMM (dual inline
memory module). If you need more RAM for your computer, you can purchase and install additional
memory upto the limit the computer manufacturer sets.
If your system responds slowly or accesses the hard drive constantly, then you need to add more RAM.
If you are running Windows 95/98, you need a bare minimum of 32 MB, and your computer will work
much better with 64 MB. Windows XP needs at least 128 MB – preferably 256 MB to run efficiently.
The amount of RAM listed for each system above is estimated for normal usage -- accessing the
Internet, word processing, standard home/office applications and light entertainment. If you do
computer-aided design (CAD), 3-D modeling/animation, picture editing or video editing, or heavy data
processing, or if you are a serious gamer, then you will most likely need more RAM. You may also need
more RAM if your computer acts as a server of some sort (Internet, database, or network).
In addition to the RAM in your system, there are other types of memory and other ways to use it. These
include ways to store more data, or store it so it can be accessed faster.
Most computers today have something like 128, 256 or 512 megabytes of RAM or system memory
available for the CPU to use. Unfortunately, that amount of RAM is not enough to run all of the
programs that most users expect to run at once.
For example, if you load the operating system, an e-mail program, a Web browser, Windows media
player and a game into RAM simultaneously, 128 megabytes may not be enough to hold it all. If there
were no such thing as virtual memory, then once you filled up the available RAM your computer would
have to say, "FULL! Sorry, you can not load any more applications. Please close another application to
load a new one."
With today’s personal computers, if a program exceeds its allocated space, the operating system uses an
area of the hard disk, called virtual memory, to store parts of programs or data files until they are
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needed. With virtual memory, what the operating system does is look at RAM for areas that have not
been used recently and copy them onto the hard disk. This frees up space in RAM to load the new
application. Because this copying happens automatically, you don't even know it is happening, and it
makes your computer feel like is has unlimited RAM space even though it may only have 128
megabytes installed. Because hard disk space is so much cheaper than RAM chips, it also has a nice
The read/write speed of a hard drive is much slower than that of RAM, and the technology of a hard
drive is not geared toward accessing small pieces of data at a time. If your system has to rely too heavily
on virtual memory, you will notice a significant performance drop. The key is to have enough RAM to
handle everything you tend to work on simultaneously -- then, the only time you "feel" the slowness of
virtual memory is when there's a slight pause when you're changing tasks. When that's the case, virtual
memory is perfect.
When it is not the case, the operating system has to constantly swap information back and forth between
RAM and the hard disk. This is called thrashing, and it can make your computer feel incredibly slow.
When it comes to access speed, processors are currently outstripping memory chips by an ever-
increasing margin. This means that processors are increasingly having to wait for data going in and out
of main memory. Even with a wide and fast bus, it still takes longer for data to get from the memory to
the CPU than it takes for the CPU to actually process the data.
Caches are designed to alleviate this bottleneck by making the data used most often by the CPU
instantly available. One solution is to use cache memory between the main memory and the processor,
and use clever electronics to ensure that the data the processor needs next is already in cache. The main
purpose of a cache is to accelerate your computer while keeping the price of the computer low. Caching
allows you to do your computer tasks more rapidly.
Primary or level 1 cache is built right into the CPU. It is very small; normally 16 kilobytes (KB) in size.
The secondary or level 2 cache typically resides on a memory card located near the CPU. The level 2
cache has a direct connection to the CPU. Depending on the CPU, the size of the level 2 cache ranges
from 256 KB to 4 megabytes (MB).
In most systems, data needed by the CPU is accessed from the cache approximately 95 percent of the
time, greatly reducing the overhead needed when the CPU has to wait for data from the main memory.
Some inexpensive systems dispense with the level 2 cache altogether. Many high performance CPUs
now have the level 2 cache actually built into the CPU chip itself. Therefore, the size of the level 2 cache
and whether it is onboard (on the CPU) is a major determining factor in the performance of a CPU.
CPU Cache RAM Virtual Memory
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Read-Only Memory (ROM)
One major type of memory that is used in PCs is called read-only memory, or ROM for short. ROM is a
type of memory that normally can only be read, as opposed to RAM which can be both read and written.
There are two main reasons that read-only memory is used for certain functions within the PC:
Permanence: The values stored in ROM are always there, whether the power is on or not. A
ROM can be removed from the PC, stored for an indefinite period of time, and then replaced,
and the data it contains will still be there. For this reason, it is called non-volatile storage. A hard
disk is also non-volatile, for the same reason, but regular RAM is not.
Security: The fact that ROM cannot easily be modified provides a measure of security against
accidental (or malicious) changes to its contents. You are not going to find viruses infecting true
ROMs, for example; it's just not possible. (It's technically possible with erasable EPROMs,
though in practice never seen.)
Read-only memory is most commonly used to store system-level programs that we want to have
available to the PC at all times. The most common example is the system BIOS program, which is stored
in a ROM called the system BIOS ROM. Having this in a permanent ROM means it is available when the
power is turned on so that the PC can use it to boot up the system. Remember that when you first turn on
the PC the system memory is empty, so there has to be something for the PC to use when it starts up.
While the whole point of a ROM is supposed to be that the contents cannot be changed, there are times
when being able to change the contents of a ROM can be very useful. There are several ROM variants
that can be changed under certain circumstances – PROM, EPROM and EEPROM
The PC Process
All of the components in your computer, such as the CPU, the hard drive and the operating system, work
together as a team, and memory is one of the most essential parts of this team. From the moment you
turn your computer on until the time you shut it down, your CPU is constantly using memory. Let's take
a look at a typical scenario:
You turn the computer on. The computer loads the basic input/output system instructions
(BIOS) from ROM.
The BIOS performs a power-on self-test (POST) to make sure all the major components are
functioning properly. It checks the RAM chips for any defects. It checks the keyboard, the
floppy drive, the hard drive, CD drive etc., the printer, and other peripherals. If it finds
something wrong, it reports an error.
The BIOS then looks for the boot sector on the sequence of storage devices identified as boot
devices in the CMOS Setup. This boot sector is another small program, and the BIOS stores it in
RAM after reading it off the device.
The Setup is stored on a CMOS chip, which is powered by a lithium battery when the computer
is turned off. The CMOS chip also keeps the date and time, so that your computer always shows
the current date and time even if it was turned off for a while. Modern systems use batteries that
are easily replaced. One factor in the battery life is how often you use your computer. While the
computer is on, it draws its power from the wall socket. When it is off, the CMOS transistors
must be kept alive by the battery. If your system consistently loses time, it could be that you
need to replace the battery. If your battery goes completely dead, it will lose all of your system
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configuration data. You might not be able to use your computer. When this happens, some
people might think they need to buy a new computer!
Booting refers to the process of launching the operating system. The BIOS will try to initiate the
boot sequence from the first device in the CMOS setup. If the BIOS does not find a device, it
will try the next device in the list. If it does not find the proper files on a device, the startup
process will halt. If you have ever left a floppy disk in the drive when you restarted your
computer, you have probably seen this message.
This is the message you get if a floppy disk is in the drive when you restart your
The BIOS has tried to boot the computer off of the floppy disk left in the drive. Since it did not
find the correct system files, it could not continue. Of course, this is an easy fix. Simply pop out
the disk and press a key to continue.
The microprocessor then begins executing the boot sector's instructions from RAM and loads the
operating system (OS) from the hard drive into the system's RAM. Generally, the critical parts
of the operating system are maintained in RAM as long as the computer is on. This allows the
CPU to have immediate access to the operating system, which enhances the performance and
functionality of the overall system.
When you open an application, it is loaded into RAM. To conserve RAM usage, many
applications load only the essential parts of the program initially and then load other pieces as
After an application is loaded, any files that are opened for use in that application are loaded into
When you save a file and close the application, the file is written to the specified storage device,
and then it and the application are purged from RAM.