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From: 252u3715@fergvax.unl.edu (Teik Leong Tan)
Newsgroups: comp.os.msdos.programmer
Subject: Re: memory
Message-ID: <252u3715.670712175@fergvax>
Date: 3 Apr 91 20:56:15 GMT
References: <1991Mar29.163548.768@maverick.ksu.ksu.edu> <1364@bragi.ctron.com>
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Organization: University of Nebraska - Lincoln
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dj@bragi.ctron.com (DJ Delorie) writes:

>.... 1024K - 1088K is usually also called "high" memory, but often
>abbreviated as the HMA for High Memory Area.  This is accessible by
>any program, but only on 286's and 386's, and only after you shut off
>gate-A20.  Himem.sys normally manages this memory.

I have seen gate-A20 being displayed on my screen before, but never
really knew what it is for. Does it mean that if A20 is disabled, then
the computer will have more access to its memory, and that this extra
memory would be available to DOS applications as expanded memory?

By the way does "high" memory refers to expanded memory only? Or does
"high" memory include both expanded and extended memory?

How can I enable or disable gate-A20?

From what I know, himem.sys only makes available 64K of high memory.
Does anyone out know of other software that would provide us with more
high memory than himem.sys, and which is relatively cheap, say free?

Many a time, my friends would come across "insufficient memory" errors
when they try to run some games. This is especially irritating when we
are in the middle of playing an exciting game.
My friend has a 25MHz 386 computer, with 4MB RAM, and 40MB hard drive.
The recommended memory needed to play the game is 590K. What I don't
understand is why is it that the computer system always restrict us only
to use the 640K conventional memory when we have a total of 4MB of
memory. So I thought "maybe the software didn't take advantage
of the available expanded/extended memory". Then I tried running the game
in the Windows 3.0 enhanced mode environment so that the computer will 
"know" that there exists these extra memory, but the game still terminates 
in the middle, giving error message "insufficient memory". So I thought
maybe the game itself has an error/bug in it, but that turns out to be
false. I tried uploading as little TSR programs as possible, thus
leaving more than 590K of conventional memory. And when I run the game,
I confront no interruptions at all -- I manage to finished the entire
game. My question here is "what are the possible causes for this
phenomena (insufficient memory) to happen?" Further explanations or
elaborations on the causes are very much appreciated.

Thank you,
Teik Leong Tan
252u3715@fergvax.unl.edu