Basics of computer architecture

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Contents see also Computer Architecture Lab A typical schematic symbol for an ALU: A & B are operands; R is the output; F is the input from the Control Unit; D is an output status At the heart of any computer, modern or early, is a (usually) simple circuit called an ALU, or Arithmetic Logic Unit. It's comprised of a few simple operations which can be done very quickly. This, along with a small amount of memory running at processor speed called registers, make up what is known as the CPU, or Central Processing Unit. A CPU isn't very useful unless there is some way to communicate to it, and receive information back from it. This is usually known as a Bus. The Bus is the input/output, or I/O gateway for the CPU. The primary area the CPU communicates with is system memory, commonly known as RAM, or Random Access Memory. Depending on the platform, the CPU may communicate with other parts of the system, or it may communicate just through memory. The "word" size of a platform is the native amount of bits that can be moved over the RAM<->CPU bus. Early computers varied on bit sizes, but most modern computers work in multiples of 8 bits, commonly known as a Byte. The first general purpose CPU on a chip, built by Intel, was the 8080 built in 1974. The 8080 used an 8 bit word, meaning it would communicate over the bus 1 byte at a time. In contrast, the 80386 has a 32 bit (4 byte) word, and the IA64 is a 64 bit (8 byte) word.

Questions for self-test What is the job of the ALU? Process information No. This answer is far too vague. What is meant by processing information?   Check security of the system No. This though this may be true on a much higher computing level.   Perform simple calculations. Yes. The job of the ALU is to perform simple calculations.   Powering up the main systems. No. The ALU is a very simple processor.

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