Virtual Memory and Control Theory

[lee at fortune.UUCP]

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