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From: jlg@lanl.ARPA (Jim Giles)
Newsgroups: net.arch
Subject: Re: VERY LARGE main memories
Message-ID: <7144@lanl.ARPA>
Date: Fri, 5-Sep-86 16:56:32 EDT
Article-I.D.: lanl.7144
Posted: Fri Sep  5 16:56:32 1986
Date-Received: Fri, 5-Sep-86 22:10:21 EDT
References: <1130@bu-cs.bu-cs.BU.EDU>
Reply-To: jlg@a.UUCP (Jim Giles)
Organization: Los Alamos National Laboratory
Lines: 33

In article <1130@bu-cs.bu-cs.BU.EDU> bzs@bu-cs.BU.EDU (Barry Shein) writes:
>...
>As I brought up once before, I still think there may be some constant
>N which completes the sentence "never buy more memory than you can
>zero out in N seconds" [I call it Shein's law of memory but some have
>claimed that Amdahl may have said something similar, great minds run
>in the same gutters :-]
>...
>A one MIP machine zeroing memory in a loop:
>
>		CLRL	R1
>	LOOP:
>		CLRL	(R1)+
>		CMPL	R1,HIMEM
>		BNE	LOOP
>
>would (theoretical machine) take 3 * (1G/1M) or 3000 seconds or
>a little less than one hour to complete. It's hard to believe
>such a machine could make -effective- use of that much memory.
>

The task of zeroing memory on the Cray 2 with 256MW (=2GB) should take
less than 5-10 seconds.  You must remember that a one MIP machine is
pathetically slow compared to a Cray (at least for vector operations
like zeroing memory, searching, sorting, and many scientific
applications).

By the way, why does everyone assume that large memory is for database
applications and such.  I can think of LOTS of scientific applications
for large memory machines - none of which involve databases in any way.

J. Giles
Los Alamos