PDP11 PeripheralsHbk 1972 - Trailing-Edge

The switches do not allow two processors to be connected together.
The switched bus may be thought of as the "output"of a bus switch, and the "in·
puts"are buses that may contain processors. One bus may be an input to more
than one switch, putting the switches in parallel. The output of one switch may be
the input to another, putting the switches in series. However, two outputs may
never be connected together. For example:
Any of the following can be easily configured with the OTl1 bus extension options:
Back-up. A back-up processor or peripheral device or even an entire backup
system, automatically takes over in the event of a failure.
Subsystems monitoring. While a subsystem is collecting data, the processor
is free to perform other tasks.
Processor failure detection. A "time-out"feature inside the switch automatically
detects a failure and switches to another processor.
Multi-processor systems. Two or more processors can operate concurrently,
with access to the same data base.
Shared peripheral systems. Costs can be reduced by having two or more
processors share peripherals. For example, a line printer, used infrequently,
is shared by several POP·11 processors. When needed by one of
the processors it is accessed quickly and efficiently with no waste of processor
power.
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