Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!decwrl!nsc!voder!tolerant!bob
From: bob@tolerant.UUCP (Bob Lee)
Newsgroups: comp.os.misc
Subject: Re: Defining virtual memory (was: a very naive Question???)
Message-ID: <2830@tolerant.UUCP>
Date: 18 Oct 88 22:44:32 GMT
References: <835@amethyst.ma.arizona.edu> <5085@medusa.cs.purdue.edu> <664@cme-durer.ARPA> <5102@medusa.cs.purdue.edu> <73039@sun.uucp> <5133@saturn.ucsc.edu>
Reply-To: bob@tolerant.UUCP (Bob Lee)
Organization: Tolerant Systems Inc., San Jose
Lines: 33

From the book "Virtual Memory Management" by Richard William Carr
(UMI Research Press), pg 2.

    The three basic elements of virtual memory, as illustrated in
    figure 1.1, are the *virtual address space*, the *main memory*,
    and the *auxiliary memory*.  Each task's program and data are
    contained in a virtual memory address space, which appears to be
    a private and dedicated area of the computer's main random-access
    memory.  In reality, the address space is only an *illusion* of
    physical memory that is created by the coordinated action of
    specialized hardware and operation system software.  In general,
    the illusion is not detectable by the task.

(The asterisks denote itallics in the original text)

The book is excellent, and has a five page bibliography at the end.
I normally don't post because by the time I read it and respond someone
else has answered quite often better than I can.  I found two things
annoying in the postings 1) the degeneration to personal attacks which
limits if not destroys dialogue and 2) it seems that no one mentioned
the "first" (earliest date I could find on a paper) system that used
virtual memory (ATLAS) or mentioned (let alone quoted) Denning, who has
done a termendous amount of work on the subject.

The above definition is not quite adequate today in the face of new
features such as shared data segments, and diskless workstations.
There is work being done at CMU in the MACH os that has a concept of
imaginary memory; however, the above definition serves as a good place
to start.

-bob
------------------------------------------------
opinions as always are my own, and should not be blamed on my company