Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!sun-barr!cs.utexas.edu!uunet!sco!seanf
From: seanf@sco.COM (Sean Fagan)
Newsgroups: comp.arch
Subject: Re: DMA on RISC-based systems
Message-ID: <2819@scolex.sco.COM>
Date: 2 Jun 89 22:01:36 GMT
References: <46500067@uxe.cso.uiuc.edu> <28200325@mcdurb>
Reply-To: seanf@scolex.UUCP (Sean Fagan)
Organization: The Santa Cruz Operation, Inc.
Lines: 39

In article <28200325@mcdurb> aglew@mcdurb.Urbana.Gould.COM writes:
>>Generally, the CPU can be a lot smarter about I/O than any brain-damaged
>>microprocessor controlled device interface.
>Smarter and faster. One of the big problems with smart I/O is that it is done
>using slow microprocessors 1 or 2 generations old. Now, if your smart I/O
>cards (1) run the latest, greatest, processors (which requires a big
>development commitment) and (2) share software with the "standard" UNIX,
>so that you don't throw out software investment when you upgrade I/O cards
>- or even move the functionality back to the CPU for some models,
>then you may have got something...   Of course, some people prefer symmetric
>multiprocessing...

Well, more than 20 years ago, a machine was built which had smart I/O
processors.  Just for the sake of fun, let's call the central processor a
"CP," and the I/O processors "PP"'s.  Fun, huh?  Now, the "CP" was 60-bits,
had something like 70-odd instructions, and was a load-store/3-address
design.  The "PP"'s were 12-bit, accumulator based machines, also with a
small instruction set.  With each "CP" you got at least 10 "PP"'s.
Incidently, the "PP"'s were a barrel-processor:  each set of 10 had only 1
ALU.

This machine *screamed*.  It had, for the time, an incredibly fast processor
(the "CP"), which, even today, will outperform things like Elxsi's.  With
the "PP"'s, it even had I/O that causes it to outperform most of today's
mainframes, at a fraction of the price.  True, it didn't run UNIX(tm)
(although I was did a paper-design of what it would take), but, if you need
the speed, it doesn't always matter, does it?

For those of you who haven't guessed, the machine was the CDC Cyber,
designed (chiefly) by Seymour Cray (God).  The machine I played on mostly
was a Cyber 170/760, which was estimated at about 10 MIPS or so, and could
support hundreds of people, all doing "real" work (database, editing,
compiling, etc.).  As I, and others, keep trying to say, MIPS are fine, but
can it do I/O?

-- 
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'.