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From: solomon@rice.edu (Richard L. Solomon)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 640K limit
Message-ID: <4308@brazos.Rice.edu>
Date: 16 Jan 90 22:57:25 GMT
References: <4668.25aed7f2@uwovax.uwo.ca> <1468@blackbird.afit.af.mil> <28808@amdcad.AMD.COM> <729@jethro.Corp.Sun.COM>
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Reply-To: solomon@screech.rice.edu (Richard L. Solomon)
Organization: Rice University, Houston, Texas
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In article <729@jethro.Corp.Sun.COM> acm@sun.UUCP (Andrew MacRae) writes:
>In article <28808@amdcad.AMD.COM> phil@pepsi.AMD.COM (Phil Ngai) writes:
>>Don't be ridiculous. The 8088 can't ADDRESS more than 1 mega. Just where
>>did you expect IBM to put the IO stuff?
>>
>>The problem is all the lazy software houses who haven't bothered to move
>>to OS/2 and take advantage of the 16 meg protected mode even though the
>>286 can handle it just fine.
>
>Simple.  IBM/MicroSoft *should* have used soft pointers to the I/O memory
>areas.

	NO....they SHOULD have mapped the I/O in the I/O ADDRESS SPACE where
it belongs......there are 64kB of I/O addresses, anyone use that much?
(Excluding VidRAM and EMS which obviously could legitimately be in the
memory address space.)  

>        They made the same mistake that was made with CP/M, hardcoding
>areas of memory for specific uses.  For those who don't remember, CP/M
>was hardcoded so that the kernal *had* to reside in the top 4kb of a 64kb
>address space, forever limiting its applications to 60kb in size.

	I beg to differ!  CP/M requires that its "kernal" (and we use that
term lightly :) ) reside at the top of the address space.  The actual
location of the CCP (user interface) was coded with just such a "soft pointer"
as suggested.  Admittedly the BDOS (2.5k) and the BIOS header table must
follow immediately after the CCP, giving a "kernal" of minimally some 5k.
Note that all of this info is for CP/M 2.2.  Beyond that, only the first
256 BYTES of memory were hardcoded - DRI was not so devious as to map
things into the MIDDLE of an address space so as to force you to buy
CP/M 9000000.......
	Also, most early CP/M systems had 16 or 32kB of memory....their
apps were limited to correspondingly less memory  :)

Richard Solomon
solomon@owlnet.rice.edu