Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!samsung!uunet!sparky!dsndata!wayne
From: wayne@dsndata.uucp (Wayne Schlitt)
Newsgroups: comp.arch
Subject: Re: Fast I/O
Message-ID: <WAYNE.91May19211810@dsndata.uucp>
Date: 20 May 91 01:18:10 GMT
References: <97b302n807vo01@JUTS.ccc.amdahl.com> <13096@pt.cs.cmu.edu>
Sender: wayne@dsndata.UUCP
Organization: Design Data
Lines: 47
In-reply-to: lindsay@gandalf.cs.cmu.edu's message of 18 May 91 05:28:40 GMT

In article <13096@pt.cs.cmu.edu> lindsay@gandalf.cs.cmu.edu (Donald Lindsay) writes:
> The Amdahl rule (1+ Mb/s, sustained, per MIP) suggests that the push
> towards 100 MHz processors is also a push past 100 Mb/s.  [ ... ]


i havent been able to find Amdahl's law stated in any of the books i
have looked at, but i cant say that i have looked real hard either... :->

if i remember correctly, it says something to the effect that for
every mips of cpu, you need 1Mb of memory and 1Mb of I/O in order to
have a "well balanced system".  


questions:

1)  are those "Mb" mega-bytes or mega-bits?

2)  what about flops?

3)  when did Gene come up with this rule?

4)  have the rules changed since the time Gene first said this?  it
    seems to me that any more you have something like 

    megabytes of memory = 2 to 4MB + 1 to 3MB/mips

    and the the i/o rate is _much_ lower than what Gene suggests.

and

5)  are there any computers that still live up to this rule?  even ibm
    mainframes have more memory than mips (especially if you count the
    memory in the disk controllers).  i really have no idea what a
    typical mainframe system has in terms of disk i/o...



i guess you could argue that "modern" computers are trading memory for
i/o, but could it be that the "old" computers were really trading i/o
for memory? 



lastly, why do i feel like asking so many questions tonight?


-wayne