Path: utzoo!attcan!uunet!sco!seanf
From: seanf@sco.COM (Sean Fagan)
Newsgroups: comp.arch
Subject: Re: SCSI on steroids, mainframes move over
Message-ID: <3238@scolex.sco.COM>
Date: 24 Aug 89 19:55:31 GMT
References: <5932@pt.cs.cmu.edu>
Reply-To: sef@kithrup.COM (Sean Eric Fagan)
Organization: The Santa Cruz Operation, Inc.
Lines: 28

In article <5932@pt.cs.cmu.edu> butcher@g.gp.cs.cmu.edu (Lawrence Butcher) writes:
>The biggest, fastest business computers seem to run 1960's operating systems
>without protection, and allow user programs to do I/O without OS assistance.
>My new question.  Is fast I/O all that micros need to bury mainframes?  Or
>is user level I/O needed?  If needed, how can simple hardware be built which
>allows direct user level DMA I/O?

CDC Cyber's don't; they do have protection (in both senses that I got from
the above paragraph).  Like other Seymour Cray machines, it doesn't have
virtual memory; instead, you have a "base address" and a "limit register"
(ba+limit is the highest memory location you can reference, and, of course,
ba is added to all address references).  However, you cannot do I/O
randomly; the peripheral processors (which hold most of the OS), won't let
you.

Fast I/O is necessary, yes, for micros to "bury mainframes"; however, you
also need a way to *use* that, which, hardware-wise, will require better
memory subsystems (so that you can do I/O to at least one memory location and
still run code at full speed).  Also, of course, you need an OS that will
take advantage of it, etc.

It will be a few years until micros can catch up; I wouldn't hold my
breath.

-- 
Sean Eric Fagan  |    "[Space] is not for the timid."
seanf@sco.UUCP   |             -- Q (John deLancie), "Star Trek: TNG"
(408) 458-1422   | Any opinions expressed are my own, not my employers'.