
                               ____________________                               Edinburgh University
                           ___________________________                           Computer Science Department


                            _________________________                            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.


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   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.

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.