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					CPU Knowledge
A computer contains several major subsystems such as the Central Processing Unit (CPU), memory,and peripheral

device controllers. These components all plug into a "Bus". The bus is essentially a communications highway; all the

other components work together by transferring data over the bus.The active part of the computer, the part that does

calculations and controls all the other parts is the "Central Processing Unit" (CPU). The Central Processing Unit

(CPU) contains electronic clocks that control the timing of all operations;electronic circuits that carry out arithmetic

operations like addition and multiplication; circuits that identify and execute the instructions that make up a program;

and circuits that fetch the data from memory. Instructions and data are stored in main memory. The CPU fetches

them as needed. Peripheral device controllers look after input devices, like keyboards and mice,output devices, like

printers and graphics displays, and storage devices like disks.The CPU and peripheral controllers work together to

transfer information between the computer and its users. Sometimes, the CPU will arrange for data be taken from an

input device, transfer through the controller, move over the bus and get loaded directly into the CPU. Data being

output follows the same route in reverse - moving from the CPU, over the bus, through a controller and out to a

device.


In other cases, the CPU may get a device controller to move data directly into, or out of, main memory.The CPU is

the main IC chip on your computer's motherboard. They come in different shapes, sizes and packages. Older CPUs

came in the DIP format, and some 286s and early 386s were QSOPs (see Integrated Circuits), but what you'll see the

most are the flat, square PGA or SPGA chips.The PGA chip used to be installed in a friction fit socket. Installation

and removal had to be done carefully to avoid bending or breaking the pins on the CPU. First, you had to line up the

chip. There is always some way to designate Pin#1, both on the chip and on the socket. There may be a dot in one

corner, or an arrow, or a small, silk-screened '1'. Usually, a CPU will have one of its corners beveled, and this has to

line up with the designated corner on the socket. You have to be sure all the pins on the chip are straight and lined up

properly, then set the chip in the socket, making sure all the pins fit into all the holes. To install the chip, you press

down firmly and evenly. If any pins aren't quite in their appropriate holes, or if you didn't push straight down, pins will

bend sideways. Trying to straighten the pins is not impossible, but usually results in them snapping off. You learn

pretty quickly to take your time and be careful. Removal is another problem.


A chip extractor is rather narrow and doesn't allow for much control when trying to lift the chip out (we're talking about

a fair amount of friction holding this chip in). Some upgrade or 'turbo' packages included a special, widened chip

extractor that was better, but still didn't provide much control. The best way is to carefully insert a narrow flat-head

screwdriver between the chip and the socket, being careful not to touch the pins underneath, and twist ever so

slightly lifting the chip a very minimal amount. Then go to the next side and do the same. By the time you work your

way completely around the chip, it'll come out fairly easy.The problem was recognized and a new Zero Insertion
Force socket (ZIF) was developed. This socket makes a big difference to the removal and installation of the PGA and
SPGA CPUs. It has a small handle or lever on the side of the socket that unclips and lifts, releasing the pins

completely. You can just lift the old CPU out, drop another in, and pull the lever down, inserting it under its little clip.

No bent or broken pins, and no chipped edges on the CPU or socket.For Intel's Pentium II, Pentium III, and some of

it's Celeron chips, the CPU is put on a small circuit board with some external cache memory, and encased or

packaged in a plastic cassette.


This 'Slot 1' style CPU clips into a connector on the motherboard called a 'Slot 1' connector.As should be obvious

now, you must match the CPU with the motherboard. Most motherboards will accept more than one type of CPU as

far as model, manufacturer, and speed is concerned, but they generally only accept one socket type. This is a

consideration that should be addressed and decided before you purchase either. The motherboard's manual will tell

you what different types of CPUs it will accommodate. If you don't have a manual, then visit the manufacturer's

website. They usually provide that type of information. The major CPU manufacturers include Intel, Motorola, IBM,

Advanced Micro Devices (AMD), and Cyrix.It should be noted that Intel was making CPUs before there were

Personal Computers. They made the first chips for IBM's PCs. Most the BIOS chips (Basic Input/Output System) on

the early motherboards were developed based on Intel's architecture. Intel is still considered to be the #1

manufacturer and has set the standard for processors.


Other CPU manufacturers and distributors tend to compare their product to Intel's, saying it's "comparable to the

Pentium II-350" or it's "better than the PIII-500". A specific CPU is described by it's manufacturer, model, and speed

in megahertz (MHz). A computer's system board has a quartz crystal on it that emits a constant signal or beat like a

metronome. Each beat is called a clock cycle and is measured in MHz, or millions of cycles per second. A CPU runs

at a multiple of the motherboard's clock speed and the instructions it performs are synchronized with each cycle of

the CPU's internal clock. So, if your CPU can perform a single instruction with each cycle, and you have a 500 MHz

CPU, then that chip can perform five hundred million instructions per second. Your heart won't beat that many times

in a lifetime. Current technology by Intel and AMD provides us with 1.5 GHz (Gigahertz) CPUs this year. That's one

and one-half billion instructions per second!


The Central Processing Unit is considered the 'brain' of your computer. It controls and directs all the activities of the

computer, transmitting, receiving and processing data constantly. But like the 'brain' of any project or organization, it

relies very heavily on its support group and advisors. There are a lot of factors involved that are related to the CPU

and have an effect on the speed and performance of your machine. Some of these factors include: Whether there's a

math coprocessor present and if it's internal or external.


The clock speed of the system and of the CPU. The amount of internal cache and external cache available. The bus

architecture or supporting circuitry on the motherboard.

				
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