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Minicomputers



[1] Until the mid-1960s, digital computers were powerful, physically large 1
and expensive. What was really needed though, were computers of less
power, a smaller memory capacity and without such a large array of
peripheral equipment. This need was partially satisfied by the rapid
improvement in performance of the semi-conductor devices 5

(transistors), and their incredible reduction in size, cost and power; all
of which led to the development of the minicomputeror minifor short.
Although there is no exact definition of a minicomputer, it is generally
understood to refer to a computer whose mainframe is physically small,
has a fixed word length between 8 and 32 bitsand costs less than 10

U.S. $100,000 for the central processor. The amount of primary storageavailable optionally in minicomputer systems ranges from 32-512K* bytes; however, some systems allow this memory to be expanded even further.

[2] A large number of peripherals have been developed especially for use in 15 systems built around minicomputers; they are sometimes referred to as miniperipherals.These include magnetic tape cartridgesand cassettes,small disk units and a large variety of printers and consoles.

[3] Many minicomputers are used merely for a fixed application and run

only a single program. This is changed only when necessary either

correct errors or when a change in the design of the system is
introduced. Since the operating environment for most minis is far less
varied and complex than large mainframes, it goes without saying that
the software and peripheral requirements differ greatly from those of a
computer which runs several hundred ever-changing jobs a day. Theoperating systems of minis also usually provide system access to either a single user or to a limited number of users at a time.

[4] Since many minis are employed in real-time processing,they are
usually provided with operating systems that are specialized for this
purpose. For example, most minis have an interrupt featurewhich allows a program to be interrupted when they receive a special signal indicating that any one of a number of external events, to which they are preprogrammed to respond, has occurred. When the interrupt occurs, the computer stores enough information about the job in process


to resume operation after it has responded to the interruption. Because 35 minicomputer systems have been used so often in real-time applications,other aspects of their design have changed; that is, they usually possess the hardware capability to be connected directly to a large variety of measurement instruments, to analog and digital converters, to microprocessors,and ultimately, to an even larger mainframe in order 40 to analyse the collected data.

* IK is defined as 210 = 1024; thus 32K = 32 x 210 = 25 x 210 = 215 = 32,768.




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