68kMLA Classic Interface

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Small extra SSE board
Posted by: MacTopus29 on 2022-10-11 11:18:02 While restoring my mac 128k I took a look at the logic board and found an extra sse board. (pictures below) Does anyone know why it is there, what it does, and if it is rare or not? Thanks
Posted by: mg.man on 2022-10-11 11:32:25 It looks like your "128k" has been after-market "upgraded" to 512k - pretty common since there wasn't a lot you could do with a stock 128k. It looks like the original "64k" RAM chips have been replaced with "256k" (now socketed) chips. That extra 'board is probably for decoding the additional address lines needed.
Posted by: Phipli on 2022-10-11 11:49:40 It looks like your "128k" has been after-market "upgraded" to 512k - pretty common since there wasn't a lot you could do with a stock 128k. It looks like the original "64k" RAM chips have been replaced with "256k" (now socketed) chips. View attachment 47460 That extra 'board is probably for decoding the additional address lines needed. View attachment 47461 I thought you didn't need extra decoding for 512k - isn't the story that they routed the extra address lines to the memory without telling Jobs?
Posted by: mg.man on 2022-10-11 11:55:04 I thought you didn't need extra decoding for 512k IDK... maybe someone here does? Both my "128k"s have been upgraded - one had a board swap (to 512k) the other an aftermarket u/g to 2Mb! That upgrade was pretty extensive to say the least!
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