Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!snorkelwacker!spdcc!ima!esegue!johnl
From: johnl@esegue.segue.boston.ma.us (John R. Levine)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 640K limit
Message-ID: <1990Jan17.031934.3374@esegue.segue.boston.ma.us>
Date: 17 Jan 90 03:19:34 GMT
References: <4668.25aed7f2@uwovax.uwo.ca> <1468@blackbird.afit.af.mil> <28808@amdcad.AMD.COM> <729@jethro.Corp.Sun.COM> <4308@brazos.Rice.edu>
Reply-To: johnl@esegue.segue.boston.ma.us (John R. Levine)
Organization: Segue Software, Cambridge MA
Lines: 19

In article <4308@brazos.Rice.edu> solomon@screech.rice.edu (Richard L. Solomon) writes:
>>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.)  

Hmmn, what did IBM actually put in the upper 384K?  Well, there's video
RAM, you want to leave that addressable for performance reasons.  Then
there's expanded memory, ditto, if you can't address it you might as well
use a RAM disk.  Then there's the system BIOS ROM and device BIOS ROMs,
again they really have to be addressable because they contain executable
code.  Gee, it looks like everything that's memory mapped really has to
be.  Oh well, it's a shame the 68008 wasn't ready in 1980.
-- 
John R. Levine, Segue Software, POB 349, Cambridge MA 02238, +1 617 864 9650
johnl@esegue.segue.boston.ma.us, {ima|lotus|spdcc}!esegue!johnl
"Now, we are all jelly doughnuts."