Acorn A500 second processor

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Acorn A500 second processor (top)

Acorn A500 second processor (bottom)

Here is a HiRes picture of the A500 second processor circuit board

I think that the A500 second processor must date from the period when Acorn were developing the Archimedes range. By connect a second processor to the Tube, Acorn could use the BBC Micro as the I/O processor and not have to worry about I/O devices on the A500.

This board has been stripped of most of it chips. The board shows the following:

• Sockets for 1 (or 4?)MB of RAM (on the right)
• OS ROMs with yellow stickers (on top). I have not yet tried to read them to see what the OS version is.
• Large square socket for ARM 1 or 2 (in middle)
• 3 small square sockets for MEMC1 (on right?) and IOC (bottom left?) and VIDC1 (top left?)
• Tube interface, scocket unsoldered (bottom next to RAM) with socket for Tube ULA above it
• White keyboard connector (middle bottom) this is the same type of connector the A500 uses
• Podule backplane connector (bottom left)
• RGB socket (top left)

These are somewhat speculative due to lack of any documentation and the rarety of the board which means I have not been able to check it elsewhere. Any further information or corrections would be appreciated.

Here is the A500 2nd processor circuit diagram.