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From: jlw@ariel.UUCP
Newsgroups: net.flame,net.unix-wizards
Subject: Paging != Virtual Memory
Message-ID: <520@ariel.UUCP>
Date: Sun, 20-Nov-83 18:47:08 EST
Article-I.D.: ariel.520
Posted: Sun Nov 20 18:47:08 1983
Date-Received: Tue, 22-Nov-83 00:20:41 EST
Organization: AT&T-ISL, Holmdel, NJ
Lines: 43

A week or so ago I posted a mild flame to net.unix_wizards
lamenting the confusion that I saw on the net regarding
the differences between a virtual memory system and a
demand paging implementation of a virtual memory system.
There were several responses on the net, some of then
quite intemperate, implying that I was incorrect, and
that, especially in academic circles, virtual memory
was synonymous with paging.  Therefore, I did some
checking.


I quote from a book actively used at Stanford at least up until
two years ago.
'The term paging is used to describe a particular implementation
of virtual memory and organization of main storage.'
Shaw, Alan C., 'The Logical Design of Operating Systems,'
pg. 117, Prentice-Hall, Inc. Englewood Cliffs, N.J., 1974.

Madnick, Stuart E., Donovan, John J., 'Operating Systems,'
pp. 139-186, McGraw-Hill, Inc. 1974.
This reference, clearly, although not as succinctly as in the
first example defines the three segment system of text, data,
and bss (blank starting segment to answer another question),
still used by BTL UNIX as an alternate form of virtual memory
management.

'The general techniques of automatically moving required program and data
blocks into physical M(ain)M(emory) for execution are called virtual
memory techniques.'
Hamacher, V. Carl, Vranesic, Zvonko G., Zaky, Safwat G., 'Computer
Organization,' p. 252, McGraw-Hill Book Co., 1978.
(all authors from Univ. of Toronto)

I hope that this will answer any questions any of you may have had.



					Joseph L. Wood, III
					AT&T Information Systems
					Laboratories, Holmdel
					(201) 834-3759
					ariel!jlw