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From: valley@uchicago (Doug Dougherty)
Newsgroups: comp.sys.ibm.pc.misc,comp.os.msdos.apps
Subject: Re: Extended/Expanded Memory Question
Message-ID: <valley.669834717@gsbsun>
Date: 24 Mar 91 17:11:57 GMT
References: <1991Mar24.033828.21204@wlbr.imsd.contel.com> <jayh.669824947@s.ms.uky.edu>
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Organization: University of Chicago
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jayh@ms.uky.edu (Jay Hofacker) writes:


>Extended memory is memory above 1 Mbyte that is directly accessable to an
>80286/386/486 in 'protected mode'.  When theses chips first boot up they are
>in 'real mode' which is completely compatible with the original 8088.  In real
>mode there is 1 Mbyte of memory total, divided into 64K segments.  MS-DOS only
>understands real mode, which is why it is limited to 1 Meg (640K because the
>video buffer starts at 640K, and the addresses above that are used for ROMs).
>In order to access extended memory, an extended memory driver must be used
>to switches the chip into protected mode, retrieve the data requested, and
>then swap back to real mode.

Bzzzzzt.  You need no special software drivers to access extended
memory.  Technically, all you need to do is set a bit in the MSW and
away you go.  Seriously, there is support in INT 15 to do the simple
tasks of storing and retrieving data to/from extended memory.  In fact,
the so-called "VDISK allocation scheme" is entirely based on INT 15.

XMS (i.e., the XMS specification) is a nice thing, but not a necessary
thing.  (EMS, on the other hand, is a necessary thing)

nit pick, nit pick...