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From: blitter@ele.tue.nl (Paul Derks)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Why is DOS limited to 640K?
Message-ID: <126@euteal.ele.tue.nl>
Date: 16 Oct 89 09:08:26 GMT
References: <8909270503.AA28536@euler.Berkeley.EDU> <10253@cbnews.ATT.COM>
Organization: Eindhoven University of Technology, The Netherlands
Lines: 20

In article <10253@cbnews.ATT.COM> rock@cbnews.ATT.COM (Y. Rock Lee,55212,cb,1J312E,6148604774) writes:
>Why is a plain DOS limited to 640K memory?
>I heard of this claim many years ago,
>but have never really understood why it has to be so.
>Today, I just ran accross the same statement on the Byte magazine.
>I am really puzzled (and bothered) by this OLD question.

DOS is NOT limited to 640k. DOS IS limited to 1 Megabyte because it runs
on an 8088/8086 and these have an address space of 1 MB. 

DOS on an IBM PC (or compatible) IS limited to 640k simply because the 
memory map of the PC only has room for 640k RAM and the rest is reserved 
for ROM's and video ram.
I have seen MS-DOS machines (not PC compatibles) with as much as
896k under DOS. These machines have only 128k reserved for ROM's and 
video memory.

Hope this clarifies things a bit.

Paul Derks