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control unit, the instructions (called the program) have to be given in
considerable detail, so the services of an expert programmer are
needed. Very elaborate computers, or special-purpose ones, have
programs built into them. They work rather like a military
organisation in which it is not necessary to give a complex multitude
of orders in detail to bring about, say, an invasion, but only a simple
Operate Plan B' which has already been worked out. These
programs are stored in the memory.
A number of different types of store are used, sometimes more
than one type in a single computer, depending on whether the stored
information is much