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From: hsu@eneevax.UUCP (Dave Hsu)
Newsgroups: net.arch
Subject: Re: Reasons For Large Main Memories
Message-ID: <147@eneevax.UUCP>
Date: Sun, 31-Aug-86 21:59:33 EDT
Article-I.D.: eneevax.147
Posted: Sun Aug 31 21:59:33 1986
Date-Received: Mon, 1-Sep-86 00:38:27 EDT
References: <8494@duke.duke.UUCP>
Reply-To: hsu@eneevax.UUCP (Dave Hsu)
Distribution: na
Organization: Imperial Widget Research Center, Kingdom of Maryland
Lines: 35

In article <8494@duke.duke.UUCP> rjn@duke.UUCP (R. James Nusbaum) writes:
>
>Some very good reasons for large main memories seem to have been ignored
>in the recent discussion.
>[deleted text about paging; large data structures]
>...  While it is true that
>sophisticated software can overcome some of the paging problems, in many
>cases the cost of more memory is less than the total cost of developing
>this software.  In todays world silicon is often cheaper than programmer time.
>
>Jim Nusbaum
>Duke University CS Dept.
>Durham,  NC

All good and well, Jim, but not the topic of discussion.  By `large' we
mean on the order of Gbytes, not Mbytes, at which point various other
factors in the system design can degrade performance substantially.
With a database of hundreds of Gbytes, the paging problems facing a
hypothetical programmer with one or two Gbytes of RAM can actually be much
worse than those facing a programmer with one or two Mbytes worth.
All it takes is a few zillion page faults, and the time lost in page-
search-and-replacement can easily exceed the time gained by a slightly
reduced number of accesses.

babbling again,

-dave
-- 
David Hsu  (301) 454-1433 || -8798 || -8715	"I know no-thing!" -eneevax
Communications & Signal Processing Laboratory	/ EE Systems Staff
Systems Research Center, Bldg 093		/ Engineering Computer Facility
The University of Maryland   -~-   College Park, MD 20742
ARPA: hsu@eneevax.umd.edu    UUCP: [seismo,allegra,rlgvax]!umcp-cs!eneevax!hsu

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