🚀 go-pugleaf

I am a VAX/VMS guru in the process of becoming an MS-DOS guru.  If these
questions sound naive, it is because I am coming at these from a strange
perspective.
In the VAX/VMS operating system, programs execute in their own virtual address
space, which gets mapped on a page by page basis into physical memory.  2 VMS
programs can be running at the same virtual address yet address different
pages of physical memory, because the mapping is done on a per-process basis
and the OS handles all that transparently.  The programmer sees 1, big pool
of RAM.

What does QEMM/386 do, from a programmers point of view?  It appears to move
things around in both physical and virtual memory.  How is this possible?
If something, say, a TSR, is moved out of low memory and into either High
Memory (By high memory, I mean the region between 640K and 1 Mbyte) or extended
memory, how does it keep working?  All of the destinations for jump instructions
would change.  Or does the 80386 have additional memory relocation?
How does QuarterDeck's OPTIMIZE program work?  Please don't say it works well,
I KNOW it works well, I've been playing with it, I can see that it works, but
don't know what it's doing or how it does it.  Well, I do know what its doing,
it's modifying CONFIG.SYS to free up more RAM in the lower 640K region.
Why does DOS have a 640Kbyte limit?
Why would anybody ever want to use expanded RAM if extended RAM is available?
If I have a "C" program which runs properly under VMS, but needs, say, 3 Mbytes
of RAM to store all its data structures, what is the best way to run it under
DOS?  Under Windows?

Sincerely yours



Jeff Silverman, Boeing.