Path: utzoo!dciem!array!colin
From: colin@array.UUCP (Colin Plumb)
Newsgroups: comp.arch
Subject: Re: Fast I/O
Message-ID: <1901@array.UUCP>
Date: 21 May 91 18:45:53 GMT
References: <97b302n807vo01@JUTS.ccc.amdahl.com> <13096@pt.cs.cmu.edu>
Organization: Array Systems Computing, Inc., Toronto, Ontario, CANADA
Lines: 16

The modern notion of a memory hierarchy rather blurs the notion of I/O
in many cases.  You've got registers<->on-chip cache<->off-chip cache<->
local memory<->shared memory<->ramdisk<->fast disk<->slow (archival) disk<->
tape<->off-site storage.

Has anyone got any rules of thumb for the apropriate sizes for these levels
and the apropriate bandwidths to them?  E.g. How fast should my local memory be
to keep up with the load from the cache?  How fast should the fast disk be to
keep up with the paging load?  How fast should the tape drives be to keep up
with backup needs?  I assume that the larger one level is, the less bandwidth
it needs to the levels below, except for uncacheable writes (I may want to
force a megabuck contract I just edited into off-site storage).

Suggestions, anyone?
-- 
	-Colin