640K limit

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Article #8554

#8554

From: Ray Dunn
Date: Fri, 12 Jan 1990 23:46

24 lines
1567 bytes

In a recent article:
>passed the 640K limit of DOS

I see this over and over again, and would like to try to put it to bed...

MSDos does *not* have a 640K limit, it has a 1Meg limit in its addressing.

640K is only an artifact of the architecture of the PC which *normally* uses
the memory map above 640K for RAM and ROM on option cards and BIOS.  If you
have for example a video card which does not occupy the A000 page with its
video memory, it is possible to map memory there to be used by DOS.

So long as the BIOS recognises it at initialization time, and reports it to
DOS, DOS will use it.

As an example, the Philips P3345 386SX based machine which allows RAM to be
mapped into any 64K segment of the A000 through E000 pages allows you to
configure with 720K of RAM available to DOS so long as you dont have a VGA
video.
-- 
Ray Dunn.                    | UUCP: ray@philmt.philips.ca
Philips Electronics Ltd.     |       ..!{uunet|philapd|philabs}!philmtl!ray
600 Dr Frederik Philips Blvd | TEL : (514) 744-8200  Ext : 2347 (Phonemail)
St Laurent. Quebec.  H4M 2S9 | FAX : (514) 744-6455  TLX : 05-824090

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Message-ID: <948@philmtl.philips.ca>

Path: arc1-ca.pugleaf.net!utzoo!attcan!uunet!philmtl!ray

References: <13346@garnet.BBN.COM> <580@watserv1.waterloo.edu>

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Path: arc1-ca.pugleaf.net!utzoo!attcan!uunet!philmtl!ray
From: ray@philmtl.philips.ca (Ray Dunn)
Newsgroups: comp.sys.ibm.pc,alt.msdos.programmer
Subject: 640K limit
Message-ID: <948@philmtl.philips.ca>
Date: 12 Jan 90 23:46:58 GMT
References: <13346@garnet.BBN.COM> <580@watserv1.waterloo.edu>
Reply-To: ray@philmtl (Ray Dunn)
Followup-To: comp.sys.ibm.pc
Organization: Philips Electronics Ltd.  Product Group PC.  Montreal.
Lines: 24

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