David Laight said:

>That would have been a VMEbus based system - the MBus/SBus ones
>were somewhat faster.  I've a 32Mbyte memory board from one of
>those - a 9u VMEbus card.

Yup, with VME and separate memory boards there would be a context switch
on every memory access.

>Those systems had a 9u 68020 based board just to perform
>system control functions, to act as a console and provide
>a slave path into system memory for VMEbus masters.

I remember that.

>I only really ever wrote X.25 for the System 25 - another
>case of the tail wagging the donkey!  I suspect the 8MHz
>286 running with zero wait state memory was faster than
>the System 25....  Might even have been able to emulate it
>faster than the host:-)

I wish I'd had that. We didn't have a network card, so I did a null
serial to another system and used UUCP to reach the network.

-- 
Rick Kelly  rmk@rmkhome.com  www.rmkhome.com