Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!wuarchive!decwrl!shelby!portia!dhinds
From: dhinds@portia.Stanford.EDU (David Hinds)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Yet another 640K question
Summary: My Mylex 386SX board recovers all of it.
Message-ID: <9095@portia.Stanford.EDU>
Date: 12 Feb 90 05:13:02 GMT
References: <5420@bgsuvax.UUCP> <NELSON.90Feb10222008@image.clarkson.edu> <1990Feb11.191736.7917@agate.berkeley.edu>
Sender: David Hinds <dhinds@portia.stanford.edu>
Organization: Stanford University
Lines: 21

In article <1990Feb11.191736.7917@agate.berkeley.edu>, ilan343@violet.berkeley.edu writes:
> How many of the 386/AT motherboards out there are able to assign the
> top 384K of the first 1M as exTENded memory?

     My Mylex MXS386 board, with an Intel/Zymos chipset and a Phoenix BIOS,
reclaims all the >640K memory that isn't used for shadowing ROM's.

> Why is the DTK machine different? Motherboard, BIOS, memory
> configuration?

     I think it depends mostly on the support chipset, which is responsible
for remapping the RAM addresses to not conflict with everything else that
goes above 640K.  Incidentally, I've found that it is best to disable any
kind of "hardware" ROM shadowing, and use QEMM to do it.  For my board,
shadowing can be switched on only for 128K blocks.  With the Phoenix bios,
only the top 32K is needed after booting - the 32K below that is only setup
code.  So, using QEMM saves 96K of RAM, and lets me remap other things into
that space.

 -David Hinds
  dhinds@popserver.stanford.edu