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From: samuels@halibut.nosc.mil (Lawrence J. Samuels)
Newsgroups: comp.sys.mac.system
Subject: Why does 24-bits => 8 MB RAM use; also a 24-bit story
Message-ID: <4112@nosc.NOSC.MIL>
Date: 14 Jun 91 15:51:47 GMT
Sender: nobody@nosc.NOSC.MIL
Organization: Naval Ocean Systems Center, San Diego
Lines: 44
Originator: samuels@halibut.nosc.mil

I'm sorry to repeat this 'frequently-asked question' (hey, maybe 
we need out _own_ FAQ list! -) ), but why, oh why, is it
that 24-bit machines, such as my IIcx, can 'use' only 8MB of
physical RAM?  As we've all heard too many times, 2^24 = 16 MB, etc., 
but in 24-bit mode, RAM above 8 MB can't be used, as I understand.
(Not fully accurate, but I want to keep the question brief.)

I thank you in advance for an answer to this question.  Perhaps I
can offer you all an amusing, but somewhat sad story in return:
Last week, my workplace had a Mac fair, vendors show up with 
products to sell us.  Apple kindly sent a fellow
to show all the good things about System 7.  I hung around
after the presentation to listen to the question asked.  A friend of
mine (possibly with ulterior motive) asked:

"How much RAM can in use in my IIcx under System 7?"

and I awaited the answers...

"You can use up to 128 MB of RAM." said the Apple representative...

...
...
(steam)
...

I had to say something... finally, I sorted of sputtered, 
"But what about the old ROMs?"  ( I didn't want to say 'dirty'.)

I got a long, blank, and somewhat hostile look (my interpretation),
then he said, "Well, 24-bit ROMs only let you use 8 MB of RAM."

Disclaimer: maybe the guy didn't hear the original question, maybe
he was trying to field a lot of stuff - but this is a touchy subject, 
you'd think he'd take greater care with a question oabout RAM use, just
in case he'd say something wrong... or maybe I'm expecting
too much.

Anyhow, it _is_ sorta funny, isn't it?

Thanks for any help with my original question!

Larry Samuels
samuels@nosc.mil