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Thread: KDF11 board question

  1. #1

    Default KDF11 board question

    All --

    I pulled an 11/23 CPU card out of my storage in advance of trying to put an 11/23 system together. The card, M8186-YA, should be the 11/23 CPU with the MMU (allowing for a 4MB memory, I think). My board has two empty chip spots, rather than one -- most images I see on-line have two chips that have two gold-topped chips (I don't know what to call these kind of piggyback chips). Is the second the MMU chip? Or maybe the FPU?

    Any info appreciated. Thanks!

  2. #2


    That extra chip is the floating point microcode. The actual FP registers are in the MMU chip.

  3. #3


    Thanks Mattis. So if the third chip is the FP chip, what's the fourth socket (second from left with the card edge down) for?

  4. #4


    I believe that's for the Commercial Instruction Set, an extension which added BCD and string instructions to the 11/23, 11/24, and 11/44. No idea how common that ever was.
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  5. #5


    The KEF11-B CIS microcode is a double size module so you could not have it simultaneously with the KEF11-A floating point option on the KDF11-A. The quad size KDF11-B has 5 sockets so on that you could have both CIS and FP.


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