Subject: PC virtual memory
Date: 04 May 94 11:58:04 EDT
From: John Foust - Syndesis Corporation <76004.1763@CompuServe.COM>

To: Imagine

Recent discussions about virtual memory on the PC seem a bit
confused.  Some of it may be due to Amiga users migrating to the PC. 
Magic is easy on the Amiga, it's tough on the PC.

There's no way to make a virtual memory add-on that will work with
any DOS program, as you can on the Amiga.  32-bit DOS programs need
what's known as a DOS extender.  Some of these merely deliver access
to all of the PC's memory, others like PharLap give virtual memory,
too.  For example, Watcom C comes with a royalty-free DOS extender. 
3D Studio uses the PharLap system.  PharLap isn't cheap, they want
$10,000 upfront and/or $20 for each program you ship that
incorporates their technology.

Decisions about memory usage and the possibility of virtual memory
must be made at the beginning, when the programmer designs the
program.  In Impulse's case, they decided to write their own DOS
extender, which makes them incompatible with almost every other
memory management scheme on the PC, as far as I've heard.  This
includes QEMM, EMM386, Windows, WinNT, OS/2, etc.




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