DM> Anyway, you would use volatile under DOS for global variables that are
 DM> modified by interrupts, or anything else modified by interrupts for
 DM> that matter.
 GD> Or another process?
 DM> Well, that's often difficult in DOS.  Even when you can - NT or OS/2 -
 DM> each DOS session should be protected from each other.
 DM> (Hey, maybe THAT's where they get this "protected-mode" buzzword
 DM> from... )
You may have something there... 
 GD> What about concurrent DOS windows?...
 DM> Are you asking about protected-mode systems?  OS/2 & NT virtualize the
 DM> screen to prevent "bleeding" (a common thing back from DESQview days).
 DM> If you think you're pointing at the video, you aren't.  The CPU, in the
 DM> current context, has been told that B000:0000, or whatever, is actually
 DM> over somewhere else.  The DOS session never knows.  ;-)  The OS is
 DM> responsible for ensuring that two DOS sessions don't both point
 DM> B000:0000 to the same place.  Of course, P-mode systems do the same
 DM> protection for ALL DOS memory (the entire 640K plus UMB, EMS, XMS,
 DM> etc.), not just the video.  The fun part comes when the DOS session
 DM> tries to play with ports owned by real (i.e., not real-mode) device
 DM> drivers.  :-)  (Don't worry - the protection is still available then,
 DM> too.)
 DM> So... I take it you don't want to write device drivers?  ;-)
No, I'll leave that to those with more time and ambition in that area...
I'll stick to *using* them... :)
Gerry Danen (gdanen@accessweb.com) C+Net BBS @ 403-477-9545
            http://www.geocities.com/SiliconValley/Way/9823
2 years, 140 days, 15 hours, 52 minutes, and 0 seconds until January 1, 2000.
... I'm in 386 enchanted mode.
--- Maximus 3.01
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