On Fri, 25 Jun 2010 22:14:00 +0100, Tim Streater wrote:

Could you define what's meant by "multiprogramming support" in this
context?

Two operating modes - user and executive. Or did I get it wrong and the
4120 had that too? Enter user mode with the EXIT instruction, and
system call back with the EXEN instruction...

Yeah, OK, that's pretty common. I guess I never heard it called that
before. But the I never used any ICL kit.

There's obvioously more, if it is to be useful, but that's a good start.

We had a Honeywell DDP-516 that had a two-mode operation, but it was
useless as (for example) there was no way of telling the previous state
when an interrupt had occurred, so you couldn't restore state. Quite a
lot of other holes too. I rewired the CPU to fix the variouls issues.



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