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Path: utzoo!watmath!clyde!burl!ulysses!harpo!ihnp4!iwu1a!david
From: david@iwu1a.UUCP (david)
Newsgroups: net.arch
Subject: Re: Why not virtual files?
Message-ID: <176@iwu1a.UUCP>
Date: Thu, 26-Apr-84 18:21:24 EST
Article-I.D.: iwu1a.176
Posted: Thu Apr 26 18:21:24 1984
Date-Received: Fri, 27-Apr-84 06:16:50 EST
References: <333@oliveb.UUCP>
Organization: AT&T Bell Labs, Naperville, IL
Lines: 20

Has there ever been an operating system that used paging to  make
disk files appear resident in main memory?  Yes, MULTICS did that
and much more.  In MULTICS  a  file  could  be  referenced  as  a
segment  in  memory or as a stream (as in the UNIX (TM) operating
system).  Pages from the file were brought into main memory  from
disk using demand paging.  MULTICS, however, went further than to
just access data files with paging--programs  were  brought  into
memory  for  execution  with  this  same  mechanism.   And when a
program made a function call that function could  be  in  another
file  which  would  be dynamically paged into memory when needed.
MULTICS demand paging therefore  eliminated  the  need  for  link
editors  and  loaders,  and  allowed  any  library to be a shared
library.

The cost for all these features was a complex  memory  management
mechanism  which  reduced  performance.   MULTICS,  however,  was
developed over ten years ago and hardware technology continues to
advance.  Perhaps it is now worth another try.

		David Scheibelhut