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Computers and Software systems A computer is a general-purpose device that behaves according to the sets of instructions and data it is provided with. Computers execute instructions to process data. Each computer has at its core a central processing unit (CPU) – these days CPUs are built as a single microprocessor chip. Examples of common microprocessors include Pentium, PowerPC, StrongARM, SPARC and Athlon. Any given computer can only execute instructions in the machine code language of its microprocessor. However, it is possible to translate instructions from one computer language to another. The details of how it is possible to translate and run programs written in Java on a variety of different types of computer (with different microprocessors) is investigated in the next unit. A high level view of a computer is that is runs a software system that accepts input, processes the input according to its instructions and produces output. The order in which input arrives and output is produced may not be predictable. Complex systems, like the Internet or like airline booking systems, are supposed never to stop once started. The simplest systems we usually call programs. They tend to have a simple structure of taking input, then processing it, then outputting something and then stoping. A computer does not distinguish between the types of low-level instructions and data it processes, but we humans need to. We need to use different strategies for working out what might be involved in complex systems and programming them than we do for simple programs.
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