Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!pt.cs.cmu.edu!g.gp.cs.cmu.edu!butcher
From: butcher@g.gp.cs.cmu.edu (Lawrence Butcher)
Newsgroups: comp.arch
Subject: Re: SCSI on steroids, mainframes move over
Summary: looking for better questions to ask about I/O
Message-ID: <5962@pt.cs.cmu.edu>
Date: 24 Aug 89 07:49:45 GMT
References: <5932@pt.cs.cmu.edu>
Organization: Carnegie-Mellon University, CS/RI
Lines: 28

A number of people have pointed out that mainframe software isn't as moldy
as I assumed.  The recently publicized American Airlines Sabre system with
more than 1200 disks online is probably not typical of business mainframes.

A 19 inch rack holding 30 700 MByte 5.25 inch disks would seem like a lot of
storage to me.  A 64 bit DRAM system giving 40 mBytes per second of data to
the I/O system while giving the processor another 40 would seem fast to me.
A computer doing 8 concurrent disk accesses would impress me.

I am however only a personal computer user.  I have no idea of what a
typical mainframe consists of.  I would like to understanding what it would
take to build an I/O and memory system which can deliver mainframe-like
performance.  For my education, could a couple of readers give me info about
systems you are familiar with?  Mainframes or supercomputers ok.
Here are some questions whose answers I do not know:

How many disk interfaces does a typical mainframe have?
How many drives per interface?
How big is the average drive?
What is the max speed of the connection from disk interface to memory?
How many transfers can happen at once?
What is a typical short term I/O rate sustained over a period of a 30 seconds?
What is a typical long term I/O rate sustained over a period of several hours?
What percentage of real memory bandwidth does the I/O system get?
What is an estimate of processor mips, to give MByte/sec / Mips?
What are better questions?

			Thanks: Lawrence Butcher