Ask a Teacher

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).

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.