Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!wasatch!cs.utexas.edu!tut.cis.ohio-state.edu!att!occrsh!uokmax!rmtodd
From: rmtodd@uokmax.UUCP (Richard Michael Todd)
Newsgroups: comp.unix.aux
Subject: Re: RAM configuration tricks on A/UX?
Message-ID: <3298@uokmax.UUCP>
Date: 4 Jun 89 01:58:33 GMT
References: <4105@emory.mathcs.emory.edu>
Reply-To: rmtodd@uokmax.UUCP (Richard Michael Todd)
Organization: University of Oklahoma, ECN
Lines: 18

In article <4105@emory.mathcs.emory.edu> km@mathcs.emory.edu (Ken Mandelberg) writes:
>I wish there was a trick that let us just add a 1 meg simm to the 4
>already there. Every Unix kernel I have seen (prior to A/UX) has been
>very flexible on sizing memory.  I don't know what the real issues are
>on the MacII, but at the very least MacOS will not boot with 5 1 meg
>simms, which gives no way to boot A/UX.
 The reason you can't just stick in a single 1meg SIMM is due to the
hardware design of the machine, NOT the OS involved.  The data bus is 32 bits
wide and the SIMMS are only 8 bits wide.  The memory bank has to be able to
present a full 32-bit word to the CPU whenever the CPU accesses it.  When you
plug in a single SIMM into the memory bank, the CPU tries to fetch 32-bit
words from memory and gets 8 bits of data and 24 bits of garbage.  It just
won't work.  That's the price you pay for having a real 32-bit processor in
your machine, instead of an 8088 :-).
-- 
Richard Todd   rmtodd@chinet.chi.il.us  or  rmtodd@uokmax.ecn.uoknor.edu  
                                    aka     ...!sun!texsun!uokmax!rmtodd
"MSDOS is a Neanderthal operating system" - Henry Spencer