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Path: utzoo!linus!decvax!harpo!eagle!mhuxl!houxm!ihnp4!fortune!lee
From: lee@fortune.UUCP
Newsgroups: net.unix-wizards
Subject: Virtual Memory and Control Theory
Message-ID: <1871@fortune.UUCP>
Date: Thu, 1-Dec-83 16:28:31 EST
Article-I.D.: fortune.1871
Posted: Thu Dec  1 16:28:31 1983
Date-Received: Sun, 4-Dec-83 03:25:25 EST
Organization: Fortune Systems, Redwood City, CA
Lines: 26

This is a comparison of real memory and virtual memory systems
vs. open-loop and close-loop control systems.  This is an attempt
to show that virtual memory systems are more effective than real
memory systems.

Real memory systems allocate resources according to programs
requirements [ open-loop systems manipulate variables in fixed
state space ].  Virtual memory systems allocate resources according
to current usages and demands [ close-loop systems steer variables 
using current states and desired paths ].  Virtual memory systems
estimate future demands with past histories, i.e. Least expected usages,
longest time to last used, etc [ close-loop systems estimate current
states using state estimators ].  Virtual memory systems response
to memory faults [ close-loop systems response to feedback error
signals ].   Virtual memory systems start trashing as ratios of
logical memory to physical memory increase [ close-loop systems
become unstable as ratios of internal state value to external
state value increase ].

It can be proven mathematically that close-loop systems response
better than open-loop systems.  It is sufficient to show that
virtual memory systems are indeed close-loop control systems.

	Ed Lee
	fortune!lee