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Date: Tue, 27 Feb 2001 18:21:03 -0700
From: Thomas Webb <tawebb AT earthlink DOT net>
Organization: WordWonder.Com
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To: opendos AT delorie DOT com
Subject: Re: Total memory? - Correction
References: <01FD6EC775C6D4119CDF0090273F74A4021FA5 AT emwatent02 DOT meters DOT com DOT au>
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Reply-To: opendos AT delorie DOT com

As I recall, 640k was the concrete ceiling on an 8088 machine. Expanded
memory was available, but it was application dependent and ugly.

"da Silva, Joe" wrote:
> 
> It's clearly been too many years and my memory bits are fading!  :-/
> 
> Obviously, I wouldn't be using EMM386 on an XT, so I guess
> it must be the kernel that checked for (and found!!!) extended
> memory on an old XT!
> 
> Another interesting bug was that, even when told NOT to use
> extended memory, the Task Switcher would still "play around"
> with the non-existent extended memory and "hang" the machine!
> 
> Anyway, enough about XT's ...   ;-)
> 
> Joe.
> 
> > -----Original Message-----
> > From: da Silva, Joe
> > Sent: Wednesday, 28 February 2001 9:45
> > To:   'opendos AT delorie DOT com'
> > Subject:      RE: Total memory?
> >
> > I don't have the luxury of so much memory to "play with", so
> > I can't verify this stuff ...   ;-)
> >
> > However, this is a BIOS interrupt, so it should report how much
> > actual extended memory exists, not how much any XMS driver
> > is able to deliver (that's what the original query wanted to find
> > out - how much actual memory existed).
> >
> > Also, AFAIK, this interrupt is safe to use on an XT/286, so a
> > check for 286+ CPU will tell you if it's safe. On this same
> > topic, and related to (the otherwise-very-very-stable) DR-DOS
> > 6.0, the kernel or EMM386 used this interrupt (IIRC) for this
> > purpose, without checking the machine type first! On my old
> > XT, this didn't actually crash the machine, but it did return
> > garbage which DR-DOS 6.0 interpreted as the amount of
> > extended memory available. Don't know if this bug was fixed
> > in latter versions of DR-DOS, but it's something to be aware
> > of, if you happen to collect PC "museum pieces".
> >
> > Joe.
> >
> >       -----Original Message-----
> >       From:   Bernie [SMTP:bernie AT mbox302 DOT swipnet DOT se]
> >       Sent:   Wednesday, 28 February 2001 4:39
> >       To:     opendos AT delorie DOT com
> >       Subject:        RE: Total memory?
> >
> >       Joe wrote:
> >       >The amount of extended memory is returned by interrupt $15,
> > function
> >       >$88. Beware however, that interrupt $15 can crash some XT machines!
> >
> >       But isn't this limited to the ammount the XMS driver can handle?
> >       I don't know the limit for DR-DOS but MS-DOS 6.x has the limit at
> > 64MB. If
> >       you copy himem.sys from 7.x you get a lot more - I haven't tried to
> > figure
> >       out the limit since 128MB "should be enough for everyone" ;-)
> >       //Bernie

--
Tom Webb
Come visit at http://wordwonder.com