Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!ucbvax!husc6!wjh12!djb
From: djb@wjh12.harvard.edu (David J. Birnbaum)
Newsgroups: comp.sys.ibm.pc
Subject: Re: AT Memory Map (spaces therein)
Message-ID: <509@wjh12.harvard.edu>
Date: 11 Jun 90 14:39:37 GMT
References: <4568@castle.ed.ac.uk> <1475@hagbard.dc.luth.se>
Reply-To: djb@wjh12.UUCP (David J. Birnbaum)
Distribution: comp.sys.ibm.pc alt.msdos.programmer
Organization: Harvard University, Cambridge MA
Lines: 29

In article <1475@hagbard.dc.luth.se> Ingvar.Strand@ext.luth.se (Ingvar Strand) writes:
>
>In article <4568@castle.ed.ac.uk> elee24@castle.ed.ac.uk (H Bruce) writes:
>>Is there any space in the AT memory map for a device such a memory mapped
>>frame grabber ? If so how much and where is it ?
>
>Assuming you have no ROM-module pluged in, there is 64kb of free memory
>at address: 0E0000 - 0EFFFF.

Not on my AT (Compuadd Standard 286/12, Phoenix 3.07 BIOS), nor on many
others.  My BIOS is a single chip at only really uses 0f800-0ffff.  But
a copy of the BIOS appears at 0e800-0efff, apparently due to a quirk
in the way the motherboard was configured in case there was a 128k BIOS.
My lim 4.0 ems board won't use the e000 segment, which means that I
can't use it for a page free, remap it with Qram, or do anything else
with it.

I posted an inquiry about this to comp.sys.ibm.pc last year and got
several reports from users with other motherboards and other bioses who
had observed the same phenomenon.  It may not affect all ATs, but you
can't count on your e000 segment being available just because it isn't
being used by the BIOS.

--David

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David J. Birnbaum         djb@wjh12.harvard.edu [Internet]
                          djb@harvunxw.bitnet   [Bitnet]
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