Path: utzoo!attcan!uunet!sco!seanf
From: seanf@sco.COM (Sean Fagan)
Newsgroups: comp.arch
Subject: Re: Historical architectural advances??
Message-ID: <8185@scolex.sco.COM>
Date: 14 Oct 90 09:19:16 GMT
References: <1990Oct4.001346.4139@Stardent.COM> <8052@scolex.sco.COM> <2750@crdos1.crd.ge.COM> <8139@scolex.sco.COM> <0KC6TSG@xds13.ferranti.com>
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Reply-To: seanf (Sean Fagan)
Organization: The Santa Cruz Operation, Inc.
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In article <0KC6TSG@xds13.ferranti.com> peter@ficc.ferranti.com (Peter da Silva) writes:
>What made the VAX a "supermini" was that it was 32-bit, rather than 16+ bit.
>This let you run problems on it that would previously have required a
>mainframe, albeit slowly.

Uhm... in that case, you could always run interpreted code, a la Sweet-16.
Doesn't make the 6502 a 16-bit machine, nor a mini-computer, though.

>As for what makes a mini/micro/mainframe... if you can hold the CPU in
>one hand (1 to a few chips) it's a micro. In two hands (1 to a few boards)
>it's a mini. Otherwise it's a mainframe. And if it's what you buy for no
>holds barred performance (extreme inflexibility in demand curve), it's a
>super.

Bzzt.  I disagree, and quite strongly.  I break things down based on
performace characteristics.

Micro, actually, I will, for the most part, agree with you.  But what about
things like the Iris family, from SGI?  They are still micros, I think
(supermicros, to be sure, but micros), even though they have multiple-board
processors (CPU, graphics, etc.).

The only reason I would still call a PDP-11 a mini is because of the I/O
performance:  it's still better than any micro I've ever seen (although I
suspect that will change soon.  I hope).

The CDC Cyber 170 state machines were mainframes, because they maximised
throughput:  high CPU speed combined with incredible I/O throughput.

A Cray YMP does not get I/O throughput to match its CPU performance; thus
it is a supercomputer, not mereley a very fast mainframe.

A mainframe should be able to handle a hundred or more users,
simultaneously, without slowing down.  A killer mainframe (not to be
confused with a killer micro 8-)) should be able to handle more than 500
users without slowing down noticeably.

A mini, on the other hand, should be able to handle 10-20 users, without
slowing down.  A super mini should be able to handle up to about a hundred
(with the distinction between a supermini and a mainframe being that the
supermini is the highend model 8-)).

A micro should be designed to be a single-user machine, even if, in reality,
several people use it.  For example, my home computer, a 25Mhz '386, can
handle 4 or 5 people logged in at once (although it does begin to get a bit
slow), but that's taxing it.

A supercomputer is a mainframe (hopefully faster than a mainframe,
actually), but without the ability to handle as many users.  For example, a
Cray is not really a multi-user machine:  it runs best with batch jobs, one
job per CPU (or one job per multiple CPU, depending on the job).  An Amdahl,
on the other hand, won't necessarily speed up too much if you are the only
person on it.  (I guess I'm talking about performance curve, here.)

This, btw, is why I don't think the VAX 780 was a supermini.  A 780 with 5
people on it, all doing CPU and I/O intensive work, can be quite painful to
be on; a 750 with more than one person on it is.  (Personal opinions, of
course 8-).)

Now, if we want to start (again) a discussion of how to improve performance
on a machine, I'm perfectly willing to post my arguments again 8-).

-- 
-----------------+
Sean Eric Fagan  | "*Never* knock on Death's door:  ring the bell and 
seanf@sco.COM    |   run away!  Death hates that!"
uunet!sco!seanf  |     -- Dr. Mike Stratford (Matt Frewer, "Doctor, Doctor")
(408) 458-1422   | Any opinions expressed are my own, not my employers'.