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Fig. 1.2 Discrete networks of mainframe and minicomputers

which access was occasionally required, or perhaps the user sometimes
had a very large task which would swamp the mini and ought to run in
the mainframe.

Suppliers of modems and multiplexers in star configurations were quick
to spot this need and developed equipment to address it. The network
then changed to that shown in Fig. 1.3. What this equipment did was to
make the users connect to a Communications Processor rather than to a
computer.

When beginning a session the user now got a message from the
communications processor, and had to tell the processor which
machine to connect to and what precise facilities were required. The
processor had knowledge of all machines and passed a message along

Fig. 1.3 Connecting the discrete networks together

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