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                                 Edinburgh University
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                             Computer Science Department



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                              Advanced Personal Machine
















     The Computer Science Department's Advanced Personal Machine is a modular
  computer system designed to allow easy experimentation with both hardware and
  software.

     Hardware components are connected by a general-purpose, moderate performance
  bus.  These components are either memories or complete processors.  The simplicity
  of the bus enables a large variety of different processors to be connected to the
  system.  The performance of the bus is sufficient to allow a modest number of
  these processors to be active concurrently.  Programs running on the processors
  communicate through the mutually accessible memory.

     In general, Input and Output devices are not connected directly to the system
  bus but are controlled by special processors.  These processors communicate with
  the rest of the system.  This approach allows such processors to be programmed to
  present a high level Input/Output interface to the other components.

     To complement the hardware, similarly modular software is being developed.
  This will allow new hardware components to use software already available on
  existing hardware components.  Thus when experimenting with, for example,
  processor architecture, it will not be necessary to write basic software such as a
  filing system in order to exercise the new hardware.







     At present, only the first basic hardware modules have been fully developed.
  These are:

  The Control Processor.
  This provides basic I/O connections to a VDU and a local area communications
  network station.  The control processor is based on a Motorola M68000
  microprocessor and in itself provides a satisfactory basis for a powerful personal
  computer.  In more developed systems, the control processor will take on the task
  of providing the necessary initialisation and control facilities for the rest of
  the system.

  The Ethernet Interface.
  This is an interface to a local area communications network, through which access
  is provided to shared facilities -- in particular to a central filestore.  It was
  developed locally and is based on the Xerox 'Ethernet' packet broadcast network.
  It transmits data at 2M bits per second.

  Memory
  A 1/2M Byte memory board has been implemented.

     Additionally several experimental graphics interfaces have been built.  Bus
  arbitration units allowing multiple processors to share the bus have also been
  built.

     25 of these systems are currently under construction for use within the
  Department.  There is also significant interest from similar establishments both


  inside and outside the University of Edinburgh.


























