Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!amdcad!sun!pitstop!sundc!seismo!uunet!mcvax!ukc!reading!minster!martin
From: martin@minster.york.ac.uk
Newsgroups: comp.arch
Subject: Re: RISC v. CISC --(really Cyber 170)
Message-ID: <595030314.2944@minster.york.ac.uk>
Date: 8 Nov 88 22:11:54 GMT
Organization: Department of Computer Science, University of York, England
Lines: 49

In article <1622@scolex> seanf@sco.COM (Sean Fagan) writes:
>In article <998@l.cc.purdue.edu> cik@l.cc.purdue.edu (Herman Rubin) writes:
>>...
>where n=[1,5].  To store a value from X<n>, you load the address into A<n>,
	 ^^^^^
actually it was n=[3,4,5] A1 and A2 were also general purpose.

>where n=[6,7].  A0 has no special values, and B0 is a hardwired 0.
>
>Ok, a few from the Wonderful World of the Cyber:
>
>	Count the set bits in a word (register or memory, it doesn't
>matter).  Very useful for some trivial applications (such as playing
>Othello), but I haven't seen much else done with it.  It was put in, it
>looks like, because the hardware was already there (in the form of parity
>checking), but I could be wrong.
>
>Sean Eric Fagan  | "Engineering without management is *ART*"
>seanf@sco.UUCP   |     Jeff Johnson (jeffj@sco)
>(408) 458-1422   | Any opinions expressed are my own, not my employers'.

The history of the population instruction is interesting: I was told (by
someone from CDC, whom I have every reason to believe knew what he was
talking about) that when Seymour Cray first designed the 6600 it did
not have the population instruction; when they showed the the machine to
the people at Los Alamos they said ``Great! We'll have 6, but only if
you add this instruction we need!''. Every machine that Seymour Cray
designed since has included the population instruction. (that was up to
the time I was told the story - can anyone verify this for the Cray-2, etc?)
It is interesting to note that the instruction set is quite nice and
regular (at the bit level), but the population instruction does not
fit into the pattern, also suggesting that it was an afterthought.

Note that the Cyber 170 is compatible with the 6600. It was an interesting
machine to program in assembler, as can probably be guessed from the above
description. However PP (Peripheral Processor) programming was much more
fun, since you have unlimited access to the main memory of the Central
Processors - the base/limit memory protection only affected CP programs.
(I'm speaking in the past tense, not because there are no more of these
machines, but because, fortunately, I don't have to program one any more!
I've still got my Compass manuals though!!)

Martin C Atkins
...!ukc!minster!martin

PS
  I leave it as an exercise for the reader (is this wise?) to guess what
Los Alamos wanted the population instruction for! But they weren't interested
in Hamming distances, rather in making bits of Plutonium go bang!!