Path: utzoo!utgpu!watserv1!watmath!att!att!dptg!ulysses!andante!mit-eddie!wuarchive!sdd.hp.com!hplabs!hpda!hpcuha!aspen!mhjohn
From: mhjohn@aspen.IAG.HP.COM (Mark H Johnson)
Newsgroups: comp.arch
Subject: Re: PR1ME 32I mode (was Re: Porting OSes (was DEC RISC Architecture))
Message-ID: <1360005@aspen.IAG.HP.COM>
Date: 17 Oct 90 23:24:51 GMT
References: <3970@goanna.cs.rmit.oz.au>
Organization: Information Architecture Group, HP
Lines: 75

/ aspen:comp.arch / pcg@cs.aber.ac.uk (Piercarlo Grandi) /  8:20 am  Oct 16, 1990 /
On 15 Oct 90 02:10:47 GMT, ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe) said:


>Maybe. But it was never supported... Or maybe it was just because the
>architects were ex-MIT/Honeywell/Multics people, even if the original
>founders were actually very much into Fortran on the original Honeywell
>minis (another sad story -- Digital was not first there).

32I mode was finally supported when Prime got the 50 series onto writable
control store so it could be fixed.  (both the fortran and C compilers 
generate good code, libraries are available.) 

The origional design was done so the box on the RFT that said "general
register architecture" could be checked.  -- They never have a second
box that asks "do you use it".  The 64V code emitted by the early
Prime compilers was so good, or the 32I code so bad, that there was
little or no gain from use of 32I in the early machines.

ok> I'm sure that PR1ME's architects were overjoyed to have a chance of
ok> getting the taste of 32V out of their mouths...

Actually 64V.  As the architect at the time, no, it worked fine.  The
folks in software seldom saw the instruction set (as it should be).
The compiler folks didn't much like either instruction set.

>Oh yeah, but for a long time 32V was *the* thing. I think indeed they
>just did it for personal pride reasons or similar. I very much doubt
>that even nowadays PRIMOS (any left? :->) and its languages run in 32I
>mode as a matter of course.

Reportedly (CSN) they sold another 360 million worth last year.  There
are a few out there still. :))

ok> Does anyone know the real story about 32I mode?

Yes, see above.  For even more fun, you should have seen the compatible 
RISC instruction set we put together...and did not build.

>Around 1982-1983 I had some contacts with Pr1me to do a port of 4.xBSD
>to their machines, my reasoning being that the only 32 bit mini
>supported by it was at the time the VAX, and just as Pr1me were
>competing with DEC in the commercial marketplace with some success
>(PRIMOS vs. VMS), the same could be expected in the technical
>marketplace (about 10% of total VAX sales at the time were for BSD).

>I would have used of course 32I mode. I was told that would not work;
>they said that PRIMOS did not use it, nobody used it (in practice only
>by special option the Fortran compiler), and so it had never been
>debugged, and so was not reliable, and they doubted very much one could
>make the machine work fully in 32I mode. They were actually very
>embarassed by this, because it meant that theirs were not really 32 bit
>systems. 

I may have been the "they".  I remember such a discussion from about then.
We looked again far later at another attempt to port Unix to 50 series.
We proved that it could be done, could use substantially all of the 
architectural features, (even the built-in process exchange after 
appropriate mods, COW, etc.) be done in 32I, and be competative to 
VAX performance.  A prototype worked reasonably well before cancellation.
(the strategic value of a 50 series running Unix in the late 80's 
was the key question.)

>Note that I had chosen Pr1me as the most likely vehicle for a VAX
>alternative not just because little to none of their sales were in the
>same market segment as that served by VAXes with BSD, but also because I
>loved their very Multics like architecture (I had even offered that I
>could make a PRIMOS simulator under BSD Pr1me such that it would execute
>PRIMOS binaries just like TWENEX could with TOPS-10 and Multics with
>GCOS/TSS ones).

The early claim was "Multics in a Matchbox" (from Bill Poduska).  Thanks
for the kind words.

Mark H. Johnson, IAG Hewlett-Packard