Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!ut-emx!kjm
From: kjm@ut-emx.UUCP
Newsgroups: comp.unix.wizards
Subject: Re: Cray I/O (was: Re: What kinds of things)
Message-ID: <13665@ut-emx.UUCP>
Date: 3 Jun 89 03:07:09 GMT
References: <873@mtxinu.UUCP>
Organization: The University of Texas at Austin, Austin, Texas
Lines: 53

Melinda Shore writes:

> Cray performance, at least on the Cray 1, the X-MP, and the Y-MP, is
> far more hampered by limited main memory.  Until fairly recently you
> couldn't get more than 8 megawords on an X and memory gets used up
> pretty quickly.  Even the 32 MW available on the Y-MP is smallish when
> you consider that you've probably got 8 processors and you've got
> several hundred users running huge jobs.

No argument so far...

> Remember also that these are
> word-oriented machines, and no instruction is smaller than 1 word (8
> bytes).

On the X-MP, at least, instructions are composed of one or two 16-bit
"parcels", thus there are two to four instructions per word.

> Swapping performance used to be pretty awful too;  I hope
> that's been fixed.

It depends on exactly how the system is configured.  It is possible to
get fairly substantial performance improvements.  There are also lots
of ways to hang oneself here.

> The whole question of the desirability of running Unix on a Cray is 
> generally brought up by batch OS people

Or by people who prefer another (interactive) operating system (I know of
one person who would like to run VMS on a Cray).

Or by people (like me) who just plain think it can be done better.
(Although not by the likes of VMS...)

> who don't know Unix and by
> Unix people who don't know supercomputing or the specifics of Cray's
> Unix implementation, which doesn't look much like Unix anymore.

Actually, I have seen lots of code sequences in UNICOS 4.0 that look a
*whole lot* like the code I read in V6...

> -- 
> Melinda Shore                                     shore@mtxinu.com
> Mt Xinu                                  ..!uunet!mtxinu.com!shore

--
The above viewpoints are mine.  They are unrelated to those of
anyone else, including my wife, our cats, and my employer.

Kenneth J. Montgomery

kjm@hermes.chpc.utexas.edu          University of Texas System
kjm@cerberus.chpc.utexas.edu        Center for High Performance Computing