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DADDY BOB'S COMPUTER Q & A
September 28,
2008
Q.
Can you explain briefly what the CPU is and
what it does in terms that a novice can
understand it?
A.
I can give a try at explaining it, but as to
how brief it is you will have to judge.
First, in a nutshell, the CPU stands for
Central Processing Unit, and is sometimes
referred to as the processor. It is the
brains of a computer. It doesn't do
everything, but in one way or another it
controls everything that the computer does.
Stopping my explanation here would do a
great injustice to the CPU.
The CPU
is the smallest removable component, the
most complex, and the most expensive
component in the computer. Its cost can
amount to half the total cost of a computer.
Below on the left is the Intel Core 2 Quad
processor and on the right the bottom view
of a different CPU, a Celeron 2.4 MHz. The
Dual 2 Quad looks similar on the bottom
except it has 775 pins. (The cost of
the Core 2 duo makes it prohibitive to
remove just to take its picture.)These CPUs measure
less then one and a half inches square.
Now to
see what is inside this case, here is a
cutaway view.
The IHS
is the Integrated Heat Shield that becomes
the top of the CPU and the TIM is the
Thermal Interface Material, a white sticky
compound designed to conduct heat. The Core
or die is a silicone wafer commonly referred
to as a chip. It has a printed circuit
etched on it making it an integrated
circuit. This is the CPU that does
all the work. Capacitors, an electronic
component can be seen in picture. As can be
seen, the core is considerably smaller than
the overall CPU case and measures around one half
an inch on a side.
The core
is just 45 nanometers
thick. A nanometer is one billionth of a
meter or one millionth of a millimeter.
To give you an idea of just how thin 45
nanometers is, by comparison a human
hair is 100,000 nanometers thick. That makes
a human hair about 2000
times thicker than this chip. The integrated
circuit etched on this tiny wafer contains over 2 billion transistors and their
connecting circuitry. Yes, that billion with
a B.
So what
is a transistor? In its very simplest form
it is just a little electronic switch that
can be turned on or off. When it is on,
current flows through it and when it is off,
it doesn't. When it is on, it is represented
by a one and when off by a zero. Remember
that everything a computer does it does with
ones and zeros.
This is
the symbol for a typical transistor. The C
is for the collector, where the current
comes in. The B is for the Base which
controls the action. The E is for the
Emitter where the current comes out. If
there is voltage applied to the Base, the
switch turns on and current flows from the
Collector to the Emitter. If there is no
voltage applied to the base, the switch
turns of and no current flows. There are
many different types of transistors, but
basically this is how they all work.
The
circuitry that is etched on the silicon
wafer looks something like this greatly
enlarged.
The 775
pins that protrude through the bottom of the
CPU's case are connected to various points
within the circuitry of this chip.
If you
looked into a modern computer case, you
would not see the CPU. When the CPU is in
use, it generates a lot of heat. Just
touching the top of a operating CPU's case would
immediately blister your finger so If allowed
to run this hot, the chip would fail very
quickly. To dissipate this heat, something
called a heat sink is used. A heat sink is
usually made out of aluminum and has fins on
it to help dissipate the heat. It is placed
directly on the CPU with thermal interface paste in between.
There is
usually a fan on top of the heat sink to aid
in this heat dissipation. This may be a
variable speed fan whose speed is controlled
by the heat passing through it. On some
computers where this CPU fan is a little
noisy due to wear, you may be able to hear
it accelerate and decelerate as the load on
the CPU varies.
To aid in
the inserting and removing the CPU on the
motherboard, a ZIF socket is used.
Pressing in a 1.5" square CPU with 755
little gold pins into tight fitting holes without
bending one of them is near impossible. ZIF
for Zero Insertion Force uses a little lever
that when raised, opens each hole so that
the corresponding pin can go in with forcing
them thus preventing damaging the CPU.
When the lever is lowered and locked, the
pins are clasped tightly, and the circuits
are completed. |
