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From: nazgul@apollo.uucp (Kee Hinckley)
Newsgroups: net.micro.apple
Subject: Re: bank switching for large memories
Message-ID: <2d4cdf02.7005@apollo.uucp>
Date: Thu, 24-Apr-86 17:26:39 EDT
Article-I.D.: apollo.2d4cdf02.7005
Posted: Thu Apr 24 17:26:39 1986
Date-Received: Sun, 27-Apr-86 05:30:28 EDT
References: <1840@ihlpg.UUCP>
Reply-To: nazgul@apollo.UUCP (Kee Hinckley)
Distribution: net
Organization: Apollo Computer Inc., Chelmsford MA
Lines: 41

In article <1840@ihlpg.UUCP> timborn@ihlpg.UUCP (Tim Born) writes:
> 
> For the 128Kb expansion, what mechanism is used?  How big are the "chunks"
> that are switched?  Are all chunks switched into the same region in the address
> spectrum, or can a 16Kb expansion coexist peacefully with a 128Kb expansion?
> Can two 128Kb expansions coexist in harmony?  Do the companies that make
> the 1 MEG (!) expansions use a different technique?  Has any sort of
> standard evolved?  I noticed that some expansion boards need a ribbon cable
> connected to the motherboard, others do not.  Why???
> 
> If anyone could shed some light on this subject, I would be most grateful.
> Would this be of general interest to the rest of the net.micro.apple?
> 

There are 3 techniques used.  One just bank switches those top 16K.  One
bank switches on the whole 64K (though you can be selective to some degree
about what gets switched (not a good idea to bank switch your stack)).
The latter is the technique used by the 64K expansion card and Applied
Engineering.  The third technique (used by Apples RAM expansion card) 
treats the memory as a device and you call it to get bytes.  Apple aside
the 64K bank switch seems to be what most people are doing.  There
is an article on all of this in a recent A+, you should read that to
be sure, my memory isn't the best.


                                            -kee

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