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From: dwc@homxc.UUCP
Newsgroups: comp.arch
Subject: Re: VM, Paging, Demand Paging
Message-ID: <1525@homxc.UUCP>
Date: Fri, 2-Oct-87 18:43:30 EDT
Article-I.D.: homxc.1525
Posted: Fri Oct  2 18:43:30 1987
Date-Received: Sun, 4-Oct-87 01:57:12 EDT
References: <8490@think.UUCP> <1745@ncr-sd.SanDiego.NCR.COM> <819@sugar.UUCP> <15250@topaz.rutgers.edu>
Organization: AT&T Bell Laboratories, Holmdel
Lines: 22

In article <15250@topaz.rutgers.edu>, ron@topaz.rutgers.edu (Ron Natalie) writes:
> The fundamental concept of VIRTUAL MEMORY is to allow the system to
> appear to have more physical memory than there is (by paging/swapping,
> whatever), hence the VIRTUAL.
> 
> It ain't virtual unless it isn't all there.
> 

i guess it all depends on where you went to school and which text
books you read.  i had always been taught that virtual memory IMPLIED
that there existed a MAPPING between virtual memory and physical memory
that was not just one to one (and onto?).

that is base register schemes also correspond to virtual memory.
paging is just another example of this.  demand paging ALLOWS for
large address spaces but you can have paging hardware without demand
paging (e.g. pre UNIX System V release ~2) and still run a virtual
memory system.  remember that this was still a win because it prevented
fragmentation of memory even though physical memory was fragmented.

danny chen
ihnp4!homxc!dwc