Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!mcsun!ukc!acorn!moncam!emmo
From: emmo@moncam.co.uk (Dave Emmerson)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 640K limit
Summary: Could have done it better...
Message-ID: <370@marvin.moncam.co.uk>
Date: 18 Jan 90 14:19:48 GMT
References: <4668.25aed7f2@uwovax.uwo.ca| <1468@blackbird.afit.af.mil| <28808@amdcad.AMD.COM|
Organization: Monotype ADG, Cambridge, UK
Lines: 33

In article <28808@amdcad.AMD.COM|, phil@pepsi.amd.com (Phil Ngai) writes:
| In article <1468@blackbird.afit.af.mil| ewilliam@galaxy-43.UUCP (Edward M. Williams) writes:
| |
| |IBM really messed things up when they designed the original PC (hindsight
| |is wonderful!) - they didn't think that anyone would ever need more than
| |640k of memory.  The original PC came with 64k!  They thought it would be 
| |safe to put all the video screen memory mappings, ROMs, and all that 
| |stuff up above the 640k line.
| |
| |Nowadays with memory capacities STARTING at 1M, the stuff between 640k and
| 
| Don't be ridiculous. The 8088 can't ADDRESS more than 1 mega. Just where
| did you expect IBM to put the IO stuff?
| 

How about at 1000:0 .. 4000:0, with 16K system RAM at 0000:0, and as
much as your processor can address from 4000:0 .. infinity.
I'm not too familiar with the 8086, but I do recall that some processors 
expect to find a hard reset vector at the top of their addressing range,
and this has to be in ROM. Even that is no excuse, properly written
relocatable soft/firmware could easily have accomodated the BIOS area
being moved. The bottom line is that everything else has followed on from
the choice of processor. That's not to say that things wouldn't have
been worse if the illustrious PC had been based on a Z80 or a 6502.
So many later decisions were made on the basis of how the mass of existing
software would cope, and of course it wouldn't have, the newer improved
PCs would have had to start from scratch. Personally I'm more inclined
to lay blame at the feet of the major software house(s) of the late 70's -
early 80's. 
It's all purely academic of course, but I guess we all need to vent some
steam now and then, and MesSyDOS sure generates some!

Dave E.