Upgrading Mac's yourself - an informed opinion

[Info-Mac]

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Subject: Upgrading Mac's yourself - an informed opinion
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Date: Fri, 20-Jul-84 23:03:56 EDT
Article-I.D.: uw-beave.1266
Posted: Fri Jul 20 23:03:56 1984
Date-Received: Sun, 22-Jul-84 03:11:33 EDT
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Organization: U of Washington Computer Science
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From: Randy Frank
the following comes from a friend at Apple. It is passed along without
further comment:

Upgrading a Macintosh to 512K Bytes is rather more complicated, at this time,
than replacing 64K Dynamic Ram chips with 256K Dynamic Ram chips. In addition
to swapping the RAM chips, at your own risk, of course, you have to add a
multiplexer in a very strange way. The current Macintosh digital boards have
a place for a seven-pin single in-line header. If the proper combination of
a multiplexer chip of the right speed and a number of pull-up resistors is
placed on a miniature daughter board with a single in-line header, and then
256K Dynamic Rams replace the 64K Dynamic RAMs, you would have a 512K
Macintosh! The ROMs are smart enough to explore the machine to see what kind
it is, and configure RAM appropriately. You will be much much better off to
wait for the Apple-label upgrade kit, which will come with a warrantee, surely.

Upgrading a Macintosh to 512K Bytes by adding three banks of 64K Dynamic RAM
is extremely unwise electrical engineering practice, unless timing margins
are very carefully examined. The RAM address line drivers are designed ONLY
to drive the capacitive load of the RAM address bus lines on the Macintosh
digital board combined with the capacitive load of the address receivers on
all RAM chips combined. Adding the wiring and the RAMs to connect three more
banks of 64K DRAM would throw the load estimates, the timing, and the whole
design way out of kilter.
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