[TUHS] (no subject)

dmr at plan9.bell-labs.com dmr at plan9.bell-labs.com
Wed Feb 22 15:08:57 AEST 2006

 > If I remember correctly, all of the "real" members of the 3B family
 > (i.e. 3B2, 3B5, 3B15 and 3B20) shared a common "virtual"
 > instruction set called (I think) IS25 - it was the job of the assembler
 > to translate IS25 into the actual machine code for the specific
 > processor used in each machine.

 > IS25 was a little curious because it only defined those instructions
 > that were likely to be of use to the C compiler - thus there was a
 > "push" instruction so that the compiler could push function arguments
 > onto the stack, but no "pop" instruction because the C compiler
 > never generated it.

IS25: just so. I managed to retrieve the scanned PDF for
the manual for this virtual instruction set.  It's an
internal memo, but I'll send it if anyone asks.  It's
2.8MB of page images and is 108 pages long.

The memories of Lindsly and Lowenstein are also apposite.
AT&T donated quite a few machines (3B20 and 3B2) to universities,
and though they appreciated the thought, there were
various drawbacks--the gift didn't include maintenance, for


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