Path: utzoo!mnetor!tmsoft!torsqnt!news-server.csri.toronto.edu!bonnie.concordia.ca!uunet!mcsun!ukc!harrier.ukc.ac.uk!zodiac.ukc.ac.uk!cur022
From: cur022%cluster@ukc.ac.uk (Bob Eager)
Newsgroups: comp.os.msdos.misc
Subject: Re: Question: only 639K available to DOS?
Message-ID: <21891.27bfa5ad@cluster@ukc.ac.uk>
Date: 18 Feb 91 10:00:12 GMT
References: <15894.27bbb58b@levels.sait.edu.au>
Organization: Computing Lab, University of Kent at Canterbury, UK.
Lines: 15

In article <15894.27bbb58b@levels.sait.edu.au>, xaandrews@levels.sait.edu.au writes:
>         Anybody come across the problem of only having 639K available to DOS?
> The DOS MEM command reports only 654 366 bytes available instead of 655 360.

If your machine has extended BIOS support, the BIOS grabs the top 1K of
available memory as the extended BIOS data area. The space in segment 40H
finally ran out!

The BIOS returns the amended value of 639K to DOS so that the 1K area is not
touched by DOS (or indeed by any other operating system, unless it isn't
going to use the BIOS).
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Bob Eager                | University of Kent at Canterbury
                         | +44 227 764000 ext 7589
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