Cray I/O (was: Re: What kinds of things)

[Steve Lamont]

In article <873 at mtxinu.UUCP> shore at mtxinu.com (Melinda Shore) writes:
>several hundred users running huge jobs.  Remember also that these are
>word-oriented machines, and no instruction is smaller than 1 word (8
>bytes).  Swapping performance used to be pretty awful too;  I hope
>that's been fixed.

One minor correction and then we can probably either move this topic
elsewhere or give it a rest.  The instructions are variable length and
may be either one or two "parcels" in length.  A parcel is 16 bits long
and, obviously, there are 4 parcels per Cray word.  Parcels may span
word boundaries.

As far as swap performance goes, I'll have to leave that to the
performance junkies.  I like my Cray time stand alone, so I don't have
to worry about all those pesky users.  I don't get it that way... but I
do like it that way... :-)

Your other comments about hyperchannel (or Ultrabus) are apt.  These
devices like large blocks of data.  Small packets can be murder,
particularly if they have to compete with, say, a mass storage subsystem
of any sort, also on the hyperchannel.  However, the productivity
enhancement of doing editing (touch up kind -- the serious text editing
belongs on a workstation) is worth it.

-- 
							spl
Steve Lamont, sciViGuy			EMail:	spl at ncsc.org
North Carolina Supercomputing Center	Phone: (919) 248-1120
Box 12732/RTP, NC 27709