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From: magik@chinet.chi.il.us (Ben Liberman)
Newsgroups: comp.sys.mac.hardware,comp.sys.mac.misc
Subject: Re: Addressable memory of 68000 (was Re: New Macs)
Message-ID: <1990Jul5.063108.14564@chinet.chi.il.us>
Date: 5 Jul 90 06:31:08 GMT
References: <316@opusc.CS.SCAROLINA.EDU> <1990Jul4.003731.336@hellgate.utah.edu> <26708@netnews.upenn.edu>
Organization: Chinet - Public Access UNIX
Lines: 23

In article <26708@netnews.upenn.edu> jeff@eniac.seas.upenn.edu.UUCP (Jeff White) writes:
>
>  On a related note, does anyone know if the 68000 can address more than 4 Megs
>of RAM (ie. is the present 4 Meg limit with Pluses and SE's a 68000 limit or
>just the way Apple designed those systems)?  

If my memory (no pun intended ;-) serves me, the 68000 will directly address
16,777,216 bytes of ram, rom...whatever (24 bit address).  The newer Motorola
chips will address 4,294,967,296 (that's 4 Gigabytes - a 32 bit address)

The 4 meg limit on SE's is just the way the board is designed (there are prob.
memory upgrade mods. out there to get you more).

The current Mac OS memory limitation of 8 meg. is a matter of Apple design.
OS space (rom and hardware address?) were mapped to start at 8 meg. because,
at the time, it was inconceivable that anyone could want more memory than that!

Computers - Life in the fast lane

-- 
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	Ben Liberman    USENET         magik@chinet.chi.il.us
	                GEnie,Delphi   MAGIK