🚀 go-pugleaf

In article <929@tucos.UUCP>, moj@utu.fi (Matti Jokinen) writes:
> >One interesting thing about the DEC 20 (and I guess DEC 10 and
> >pdp-6 as well) is that the registers are the first 8 or 16 locations in the
> >main memory map.  Does anyone know if code can be run in the registers?  And
> >if so, does it execute any faster than if it was in normal memory?
> 
> Yes, it could be done and it was considerably faster at least in the older
> DEC-10 models.  I remember reading that a separate register set was not an
> essential part of the architecture --- if it was removed, the first 16 words
> of the main memory were used instead and the machine still functioned
> correctly, only more slowly.
> --
> Matti Jokinen


This is true of all the PDP-10 processors. As I remember, the KA-10 had one
block of fast registers and swapped them when it did a context switch. The
KI-10 model had 4 sets of fast registers, 2 were reserved for real-time
processes, 1 was for normal user mode and one was for the monitor. There is a
switch to disable fast memory as well as a switch to force the diagnostics to
use a particular set. I remember a case we had that the monitor would crash
whenever we tried to re-boot with an error indicating a problem in the register
set. The diagnostic routine worked fine. After going around with the CE's, I
forced the diagnostics to use the register set for the monitor (set 1 as I
remember) and lo and behold, we discovered a register always picked a bit.


(BTW, we will finally decommission our KI-10 system in September...sigh)
Richard H. Miller                 Email: rick@bcm.tmc.edu
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