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10/06/2002 - Editorial: How Does A Processor Work? by Saeed Amen

Everyone knows a processor is the heart of a computer. Before I began my degree course in Mathematics and Computer Science, that was all I knew about processors! The actual general architecture of a processor has remained the same for over fifty, and was invented by Von Neumann. The processor is made up of several components itself. Firstly we have data registers, which are essentially very high speed memory bits. In most computers there'll be no more than a handful. Data is transfered to and from the registers via a bus linked to the RAM. This fetching of data from RAM is the slowest part of the execution cycle, and is known as the Von Neumann. Then we have the Arithmetic Logic Unit, which actually runs the programs. Most chips have basic arithmetic functions and a few more memory manipulating instructions. From these few functions, the chip does just about anything! All chips use the Fetch-Execute cycle, whereby, instructions and data are fetched from memory, and then executed.

To program a chip directly, you use Assembly language. Each processor family, has a different assembly language. It is very tedious, and is used very rarely, because these days compilers translate code into 1s and 0s that the processor can understand. However, it's important that every computer scientist writes at least one assembly language program in his/her life! As processor's have evolved they have added extra components and instructions to there arsenal. For example, as well as registers, processors now have cache, generally less than one megabyte of memory directly on the processor, which is a lot faster than RAM, but slower than registers. The idea of cache is to reduce the effect of the Von Neumann bottleneck. If you want to learn more it's a good idea to begin by understanding simpler chips like the 68000 and then moving to the modern processors.