Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!sco!seanf
From: seanf@sco.COM (Sean Fagan)
Newsgroups: comp.arch
Subject: Re: ATTACK OF KILLER MICROS
Message-ID: <3467@scolex.sco.COM>
Date: 21 Oct 89 06:41:07 GMT
References: <35825@lll-winken.LLNL.GOV> <2121@brazos.Rice.edu> <35897@lll-winken.LLNL.GOV> <9078@batcomputer.tn.cornell.edu>
Reply-To: seanf@sco.COM (Sean Fagan)
Organization: The Santa Cruz Operation, Inc.
Lines: 33

In article <9078@batcomputer.tn.cornell.edu> kahn@tcgould.tn.cornell.edu writes:
>The Cray-XMP is considerably slower than the YMP.  
>The single-processor XMP is no-longer a supercomputer.
>Take a program requiring more than 128MBytes of memory (or 64 MBytes
>for that matter (but I personally prefer more than 256M to excerice the
>VM system alittle!)) (i.e. a relatively BIG job, a *supercomputer* job)

What?!  Uhm, excercising the Cray's VM system is definitely going to be an
interesting job -- Seymour doesn't *believe* in VM!  (Well, anecdote has it
that he doesn't *understand* it 8-).)

I have mixed feelings about VM (as anybody who's seen more than three of my
postings probably realizes 8-)):  on one hand, yes, getting page faults will
tend to slow things down.  However, the system can be designed, from a
software point of view, in such a way that page faults will be kept to a
minimum.  Also, having about 4 Gbytes of real memory tends to help.  And,
face it, swapping programs in and out of memory can be a time-consuming
process, even on a Cray -- if you're dealing with 100+ Mword programs!

Other supercomputers have VM, of course.  However, I have never gotten the
chance to play on, say, an ETA-10 to compare it to a Cray (I asked someone,
once, at FSU for an account, and I was turned down 8-)).  My personal
opinion is that the machine is not as fast for quite a number of
applications, but having the VM might help it beat a Cray in Real-World(tm)
situations.  Anybody got any data on that?

And, remember:  memory is like an orgasm:  it's better when it's real
(paraphrasing Seymour).  8-)

-- 
Sean Eric Fagan  | "Time has little to do with infinity and jelly donuts."
seanf@sco.COM    |    -- Thomas Magnum (Tom Selleck), _Magnum, P.I._
(408) 458-1422   | Any opinions expressed are my own, not my employers'.