From:	billg <enloop AT bellsouth DOT net>
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Newsgroups:	comp.os.msdos.4dos,comp.os.msdos.apps,comp.os.msdos.desqview,comp.os.msdos.djgpp,comp.os.msdos.mail-news
Subject:	Re: regarding dos 640kb barrier
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NNTP-Posting-Date:	Mon, 11 Aug 2003 15:55:25 EDT
Date:	Mon, 11 Aug 2003 16:06:32 -0400
To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

yogesh wrote:
> everybody knows that dos has 640kb barrier..and hence this makes dos
> inefficient...

It isn't DOS, it's the chip it was designed to run on.  The 8088/8086 
can address one megabyte of memory. No operating system running of an 
8088/8086 can run code above above the 1-meg line. (Chips that can go 
into protected mode can use memory above 1-meg as expanded or extended 
memory, but not as space in which to execute code.)

IBM's PC architecture put their ROM BIOS, video memory, etc., in a chunk 
of memory starting at 640k.  Hence, the 640 k limit. Those things had to 
be within the address space of the 8088/8086, and would have taken the 
same amount of memory regardless.

Interestingly, the immediate successor to the 8086, the 80286, could go 
into protected mode and address much more memory.  Although that ability 
was largely ignored and the chip was used as a faster 8086, one wonders 
what would have happened had DOS orignally been coded for a 286 box.

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