Newsgroups: comp.arch
Path: utzoo!utgpu!watserv1!vlsi!ward
From: ward@vlsi.waterloo.edu (Paul Ward)
Subject: Re: Can old architectures run fast?
Message-ID: <1991May9.144406.20558@vlsi.waterloo.edu>
Organization: University of Waterloo
References: <c506634.3284@umcvmb.missouri.edu>
Date: Thu, 9 May 1991 14:44:06 GMT
Lines: 43

In article <c506634.3284@umcvmb.missouri.edu> 
            c506634@umcvmb.missouri.edu (Eric Edwards) writes:
>In article <1991May7.130302.22332@vlsi.waterloo.edu> 
            ward@vlsi.waterloo.edu (Paul Ward) writes:
>>  
>> A meaningless question - how can you possibly compare price performance of
>> a workstation (typically a single or a few user machine) with an IBM 
>> mainframe which can support 400+ users concurrently?  If anything, the 
>> major difference between PCs, workstations, minis and mainframes is the 
>> I/O bandwidth, not the processor performance.  What good is 500 MIPS 
>> and 50 MFLOPS if you are waiting so long for an I/O operation to complete 
>> that the real performance is~5 MIPS and 0.5 MFLOPS.  (The same applies 
>> to the memory subsystem - you have
> 
>It's not entirely meaningless.  Many jobs are CPU, not I/O bound. 
>Compatibility aside, you would have to be a fool to use an IBM mainframe
>for that.   They don't even come close to competitive with workstations on
>CPU performance.  Can *all* the price performance difference be attributed
>to the presence or absence of a high speed IO system?  

I agree that many jobs are CPU bound - but take a closer look at them.  Take
simulation as an example - suppose you want to simulate 10,000,000 logic
gates in some design.  (BTW there is nothing on the market that can do this
at the moment).  It looks like a classic CPU bound problem.  However, it is
so large, that no workstation memory system can handle it.  You need virtual
memory.  But again, it is so large that you will spend forever just swapping
pages between disk and memory.  What is required is a very large (~100s MB) of
memory, and a very fast disk I/O subsystem.

>Also, is there anything to prohibit a RISC based machine from having a high
>speed IO subsystem?  Would adding this make the machine cost as much as a
>3090?

I don't know, but it is an interesting question.  Do you have $20,000,000 ?
We can try a little experiment.  :-)

Paul Ward
University of Waterloo


-- 
"One can certainly imagine the myriad of uses for a hand-held iguana maker."
								-  Hobbes.
