Newsgroups: comp.sys.ibm.pc
Path: utzoo!utgpu!jarvis.csri.toronto.edu!csri.toronto.edu!il
From: il@csri.toronto.edu (Indra Laksono)
Subject: Re: 640kb limit on DOS?
Message-ID: <8812160414.AA14373@yorkville.csri.toronto.edu>
Keywords: PS-2/50 DOS
Organization: University of Toronto, CSRI
References: <8043@ihlpl.ATT.COM> <3521@nicmad.UUCP> <196@nbires.nbi.com>
Distribution: na
Date: Thu, 15 Dec 88 23:14:14 EST


>I guess I better not tell this to my Tandy 2000 with 768K of memory or my NBI
>2000 with 800K of DOS memory.
>
>The problem is that PC clones have video memory starting at 0C000h which limits
>contiguous low memory (The only memory normally used by DOS) to 640K.  This is

I think you have it backwards.  If you have video memory starting at C0000h,
then, assuming that you are able to use everything below this, you will
have 12x64K=768K of CONTINGUOUS memory.

>a design limitation that made sense when the PC was first introduced with only
>64K of memory and 640K seemed like more than you would ever need in a PERSONAL
>computer.
>

The ega has video ram starting at A0000h (4 zeros, not 3), this would
mean that only 640K is ever usable in a system with ega.  Though it is
doubtful if ms designed msdos with ega in mind way back then, still
The MDA was introduced way back and it had display memory at B0000
or B8000 (I forgot).





