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The Chip at the Heart of a Computer
The word "chip" is commonly used to refer to an integrated circuit. Microprocessors are one of many types of integrated circuits. The microprocessor is central to the functioning of a computer. It is used to process information by keeping all the parts of the computer working together to complete a given task. The microprocessor is the most complex and expensive of the chips needed to make a computer work.
Today's microprocessors may contain tens of millions of transistors and other electronic components, yet be smaller than your thumbnail. Today's microprocessors work very rapidly and are very reliable.
Microprocessor functions can be described as a simplified three-step process. The fetch step involves getting an instruction from the computer's memory. The decode step involves deciding what the instruction means. The execute step involves carrying out the instruction. A modern microprocessor can complete this three-step process many millions of times in a single second. Special areas on the microprocessor are designed to enable the computer to complete these three steps.
Each type of microprocessor has its own design and organizational scheme. However, all microprocessors must perform similar tasks. The transistors—the building blocks of the microprocessor—are arranged in circuit groups. Each circuit group is designed to perform a specific task. The following circuit groups are needed to allow the microprocessor to perform the fetch, decode, and execute operations:
Arithmetic Logic Unit: A set of circuits dedicated to numerical calculations and logical operations
Control Unit: Circuits that control the sequence of the processing done by the microprocessor and hold the instructions in the correct sequence until needed
Decode Unit: Circuits used to translate the instructions into control signals and directions, and hold them in sequence until they are requested by the control unit
External Bus Unit: Pathway provided to move data to and from the microprocessor
Internal Bus Unit: Circuits that manage the flow of information from one part of the microprocessor to another
Memory Management Unit: Circuits designed to keep track of information that has been processed, reclaim the space when the instructions are done, and help organize the way instructions and data are stored
Because every microprocessor uses the fetch, decode, and execute cycle, the internal circuit groups of most microprocessors perform very similar functions. The special circuit areas work together to accomplish the three steps. The general areas used for fetch, decode, and execute on an Intel® Pentium® III microprocessor are located as indicated in the diagram.
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| The surface of a Pentium® chip with the special areas for fetch, decode, and execute indicated. |
Each instruction that a microcomputer can execute is quite simple. For example, a typical instruction that the microprocessor can understand is "add two numbers." Another instruction is "compare two numbers to see if one number is larger than the other." A typical microprocessor has about 150 different built-in instructions with the necessary circuitry to decode and execute them.
Microprocessors neither think nor reason. They simply follow the instructions given to them by software programmers. The smallest error in such a set of instructions can lead to large errors in the final results produced by the computer.
Programmers try hard to avoid errors in the software they write. However, it is difficult to write long programs without making mistakes. In large software companies, many programmers are employed just to test the software that others write. These programmers work to find any errors in the software.
An error in a computer program or computer hardware is called a bug. The process of detecting and correcting an error in a computer program is called debugging the program. Computer programmers spend a lot of time testing and debugging the programs they write.
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