Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.csd.uwm.edu!cs.utexas.edu!uunet!sco!seanf
From: seanf@sco.COM (Sean Fagan)
Newsgroups: comp.arch
Subject: Re: PC vs. mainframe I/O (Re: SCSI on steroids)
Message-ID: <3289@scolex.sco.COM>
Date: 10 Sep 89 07:50:14 GMT
References: <21962@cup.portal.com>
Reply-To: seanf@sco.COM (Sean Fagan)
Organization: The Santa Cruz Operation, Inc.
Lines: 89

In article <21962@cup.portal.com> cliffhanger@cup.portal.com (Cliff C Heyer) writes:
Lots of misconceptions.

>Remember 1960s computers had a *blazing* 1/2 MIPS 
>and about 500KB core. 

Hmm.  360's and 370's, which are from the '60's, certainly had more than
that.  CDC Cybers, with which I am most concerned (of course 8-)), also had
more than that (256Kwords of memory, 3-10MIPS / MFLOPS).

>"Mainframe I/O" where you have 100+ channels 
>cooking at 3MB/sec does not mesh with a 
>timesharing-type OS. 

*What*?!  It works *best* with a timesharing OS, because it's more likely to
be utilized!

>That's why IBM LAYERS all 
>it's timesharing environments(CMS, TSO) ON TOP of 
>MVS or VM (and they run slow as death). You can't 
>always have your cake and eat it too. 

CDC's NOS, which runs on CDC 170-state Cybers, is an interactive (of sorts
8-)) timesharing OS.  True, it was based on a batch system, but it is now a
true TSOS, and it is *very* efficient.  In fact, I believe that NOS nowadays
is more efficient (for I/O, running jobs, etc.) than the last version of the
batch-only OS was...

>The OS has 
>to be created for the application. 

Not necessarily.  Witness UNIX, which can, with a few modifications, be
*very* quick and efficient.  I, personally, think Mach is going in the
correct direction.  If you make your OS do minimal work, efficiently and
properly, everything else falls out as a library, which need not be used.
What you're talking about is running a *single* job on a computer, and this
is not cost-efficient anymore (not for minis and higher, I don't believe).
It is cheaper to have a slightly slower OS and application pair.

>ALSO keep on mind the the alleged "100+ MIPS" 
>processors are actually multiprocessors. The IBM 
>3090-600 has 6 15 MIPS processors. The *fastest* 
>single user processing is 15 MIPS - NOT 100 MIPS! 
>IBM's max uniprocessor MIPS is about the same as 
>others in the industry.  

Not everybody has that problem.  CDC Cybers are blazingly fast; no single
CPU version gets 100+ MIPS, but they are very fast, faster than 15 MIPS to
be sure (I think the 990 [single CPU] gets something like 50-60 MIPS /
MFLOPS).

Don't think that the way IBM does it is the way it has to be done.  As the
saying goes, there's more than one way to skin a cat...

>Yes, the only thing that distinguishes an 8-MIPS 
>PC board from an 8-MIPS VAX 6000 board is the I/O 
>bandwidth. This comes primarily from the memory 
>cycle time.

Not really.  It comes from the memory bandwidth, which is a bit different
(ok, not a whole lot, but a bit).

>If you were to buy a PC with minicomputer or 
>mainframe I/O - it would cost you as much as a 
>minicomputer or mainframe. Because the 
>*engineering* costs & material costs will be the 
>same as the big guys. You'd have to have a *fast* 
>memory subsystem which would cost *bug bucks*.

Naturally.  It also wouldn't be PC compatable (bus-wise).  However, both MCA
and EISA offer some interesting possibilities (I haven't seen anybody *use*
them, so there might be good reasons for that) in Real(tm) I/O.

>[the first] disk in the late 50s contained 5MB? NOT 50KB like 
>early floppies. These guys new how much data they 
>had to store and weren't going to fuss around with 
>a 50KB hard drive.

Did you know how *large* the think was compared to a floppy?  That's why the
floppy exists:  as an alternative to hard disks (well, there are, again,
some other reasons, but that's what it can be considered as).  If you're
going by that reasoning, you should also point out that the tape drives held
several hundred megabytes.  Are they a viable alternative?  No.  Different
needs, different uses, different solutions, different markets.

-- 
Sean Eric Fagan  | "Time has little to do with infinity and jelly donuts."
seanf@sco.COM    |    -- Thomas Magnum (Tom Selleck), _Magnum, P.I._
(408) 458-1422   | Any opinions expressed are my own, not my employers'.