CPU Central Processing Unit

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					CPU - Central Processing Unit
CPU - Central Processing Unit The CPU or Central Processing Unit is the "brain" of the computer,
it is the 'compute' in computer. Without the CPU, you have no computer. Computer CPU's
(processors) are composed of thin layers of thousands of transistors. Transistors are tiny, nearly
microscopic bits of material that will block electricity when the the electricity is only a weak
charge, but will allow the electricity pass through when the electricity is strong enough. The
transistors within the CPU transition from being a non-conductor (resist the electricity) to a
conductor (they conduct electricity) when the electrical chage is strong enough. The material
that CPU transistors are made of loses its resistence to electricity and becomes a conductor
when the electricity gets strong enough. The ability of these materials (called semi-conductors)
to transition from a non-conducting to a conducting state allows them to take two electrical
inputs and produce a different output only when one or both inputs are switched on. A
computer CPU is composed of millions (and soon billions) of transistors. Because CPU's are so
small, they are often referred to as microprocessors. So, the terms processor, microprocessor
and CPU are interchangeable. AMD, IBM, Intel, Motorola, SGI and Sun are just a few of the
companies that make most of the CPU's used for various kinds of computers including home
desktops, office computers, mainframes and supercomputers.



Modern CPU's are what are called 'integrated chips'. The idea behind an integrated chip is that
several types of components are integrated into a single piece of silicon (a single CPU), such as
one or more execution cores, arithmetic logic unit (ALU) or 'floating point' processor, registers,
instruction memory, cache memory and the input/output controller (bus controller).



Each transistor is a receives a set of inputs and produces output. When one or more of the
inputs receive electricity, the combined charge changes the state of the transistor internally and
you get a result out the other side. This simple effect of the transistor is what makes it possible
for the computer to count and perform logical operations, all of which we call processing.



A modern computer's CPU usually contains an execution core with two or more instruction
pipelines, a data and address bus, a dedicated arithmetic logic unit (ALU, also called the math
co-processor), and in some cases special high-speed memory for caching program instructions
from RAM.
The CPU's in most PC's and servers are general purpose integrated chips composed of several
smaller dedicated-purpose components which together create the processing capabilities of the
modern computer.



For example, Intel makes a Pentium, while AMD makes the Athlon, and Duron (no memory
cache).



CPU Generations



CPU manufacturers engineer new ways to do processing that requires some significant re-
engineering of the current chip design. When they create this new design that changes the
number of bits the chip can handle, or some other major way in which the chip performs its job,
they are creating a new generation of processors. As of the time this tutorial was last updated
(2008), there were seven generations of chips, with an eighth on the drawing board.



CPU Components



A lot of components go into building a modern computer processor and just what goes in
changes with every generation as engineers and scientists find new, more efficient ways to do
old tasks.



Execution Core(s)

Data Bus

Address Bus

Math Co-processor

Instruction sets / Microcode

Multimedia extensions

Registers

Flags
Pipelining

Memory Controller

Cache Memory (L1, L2 and L3)

				
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