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Path: utzoo!watmath!watnot!watdaisy!dvadura
From: dvadura@watdaisy.UUCP (Dennis Vadura)
Newsgroups: net.arch
Subject: Re: Page size and the meaning of life
Message-ID: <7459@watdaisy.UUCP>
Date: Mon, 21-Oct-85 20:51:43 EDT
Article-I.D.: watdaisy.7459
Posted: Mon Oct 21 20:51:43 1985
Date-Received: Tue, 22-Oct-85 05:39:15 EDT
References: <926@decwrl.UUCP> <931@lll-crg.ARpA>
Reply-To: dvadura@watdaisy.UUCP (Dennis Vadura)
Organization: Computer Science Dept., University of Waterloo
Lines: 26
Summary: 

In article <931@lll-crg.ARpA> brooks@lll-crg.UUCP (Eugene D. Brooks III) writes:
>Would anyone care to comment on why we need virtual memory at all
>with a 256 meg real memory being available in the near future?
>
>I don't see the need for it.

One need for virtual memory is to be able to support relocatable
code which has non-relative addressing references.  A good example
is most C compilers.  They tend to locate the program constants
at virtual address 0 and up, with access being by direct addressing.

In a multitasking environment virtual memory can be used to protect tasks
from illegaly accessing each others data space.  Further it allows tasks
to share in a controled manner portions of their respective address spaces.

Perhaps the question to ask is do we need disk paging?
With large memories becoming available rolling pages out to disk may become
unneccessary, but the concept of virtual memory and its associated attributes
is probably still useful.

-- 
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Dennis Vadura, Computer Science Dept., University of Waterloo

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