18 Mar
2004
18 Mar
'04
2:10 p.m.
KA620 is something I've heard about, but never
figured out exactly
what it was. It was some kind of slightly hobbled KA630, wasn't it?
Yes.
Maybe a KA630 w/o FPU?
No.
Does anyone know?
I do. I wrote a semi-embedded minikernel to run on one.
A KA620 is the same as a KA630 except that the P0 and P1 page tables
are looked up in physical memory rather than system virtual memory.
(Loosely put, P0BR and P1BR need to be physical addresses rather than
system-region virtual addresses.)
The story I heard was that customers wanted CPU baords for multi-CPU
machines, but DEC was very paranoid about people buying CPU boards and
building cheap knockoff machines with substandard backplanes &c.
As a result, DEC made it very hard to get a KA630 without a full system
around it. But the KA620 wouldn't run VMS, so people couldn't build a
knockoff VAX around it - or so the thinking went as it was explained to
me - and thus was safe to sell on its own.
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