The Central Processing Unit (CPU)

Essay by MohammedHHigh School, 12th gradeA-, May 2004

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The Central Processing Unit (CPU)

What exactly is a CPU? If you opened up a Mainframe or a Supercomputer the answer you would get could surprise you. These machines hav lots of printed circuit boardsheld in framed cases and connected by endless metres of cables to form their CPUs.

Looking into a PC is much simpler - you can find an identifiable chip as the CPU. Another surprise is that, for all their physical differences the CPUs of both PCs and Supercomputers have in common.

The Operation of the CPU

Every processor has its own set of instructions (instruction set) that it can recognize and execute. These instructions are low-level instructions, such as add, subtract, multiply and divide. They work directly with the processor and communicate with the basic capabilities of the processor.

Data and sequences of instructions (known as programs) are stored in memory. The working part of the computer is the CPU which is separate from memory.

Instructions and data is transferred from memory into the CPU. When they get there thew CPU actually has to carry out the instructions and processes the data.

The CPU deals with each instruction in a series of steps - these steps repeated fro every instruction that it gets processed so the series of steps is called a 'cycle'. The cycle os called the machine cycle. Each machine cycle involves

Fetching an instruction from memory,

decoding an instruction,

transferring data and

executing the instruction.

As you can see the machine cycle is not a simple one-step process. This means that the CPU cannot be simple, one component device.

Components of the CPU

Al CPUs are divided into parts that do specific jobs. These parts are actually made up of many components but, for the sake of simplicity, we are going to...