The CPU (Central Processing Unit)
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
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
The bus architecture or supporting
circuitry on the motherboard.
I'm going to talk about the Central Processing
Unit a bit more later, but to help you better understand the
changes, improvements and history of the microprocessor and
your computer, let's spend some time on the above support group.