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MathGroup Archive 1995

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Re: OS2 Version, Use of Virtual Memory?

  • To: mathgroup at christensen.cybernetics.net
  • Subject: [mg1571] Re: [mg1559] OS2 Version, Use of Virtual Memory?
  • From: John Fultz <jfultz>
  • Date: Sat, 1 Jul 1995 02:08:03 -0400

> Could someone please explain how Mathematica for OS2 uses virtual   
> memory?  Is it capable of swapping out active blocks of memory? 

In OS/2, as in Windows, virtual memory is a function of the operating system.
Functional details of virtual memory, such as swapping pages of memory to and
from the hard disk, are handled by the operating system and are invisible to
user programs, including Mathematica.  So, in essence, you are actually asking
if OS/2 can swap out active blocks of memory for running programs.  Yes, it
can, as can Windows, although OS/2 has fewer limitations (see below).

> For example, suppose I am creating a large Table using Solve.  Is this   
> version capable of swapping out intermediate results so that the   
> calculation can be completed? 
>  
> I am currently using 2.2.4 for windows (but have ordered the OS2   
> version).  On this platform (running under Warp) I have been getting   
> "Unhandled Memory Faults" and "Out of memory, Exiting messages."    
> One of the tech folks suggested that I rewrite the program without the   
> Solve command since this creates alot of intermediate values.  I did this   
> and am still getting the error (plus things slowed down by a factor of 10   
> !).  The problem is recursive so things get real big, real fast. 
>  
> Anyway, wondering if there is any reason to believe that the OS2 version   
> will handle this stuff any better. 

There are limitations which might, indeed, make a difference.  As I
understand it, Windows memory requests can be no larger than 16
megabytes.  While a Windows program can make multiple requests of 16
megabytes, if Mathematica creates a single data structure larger than
16 megabytes, you're going to be in trouble.  OS/2 is not nearly so
limited in this aspect.

Also, Windows limits the size of your swap file, by default, to be
about 4 times the size of your physical RAM or to about half the free
space on your disk drive, whichever's smaller.  OS/2, on the other
hand, will by default use all but 4 megabytes of your designated swap
drive.

So, if your problems happen to fall under any of these constraints, OS/2
would be better.

> Thanks,
> 
> Ezra D. Greenberg 
> Department of Economics
> University of Maryland at College Park
> edg at wam.umd.edu

John Fultz
Wolfram Research, Inc.


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