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Thread: IBM AT: How do you install 256KB RAM with a type 2 or 3 motherboard?

  1. #1

    Default IBM AT: How do you install 256KB RAM with a type 2 or 3 motherboard?

    It only has one bank, does it take 128K chips as well? I'm not getting anything with google or forum search. Looked on Modem7's site, perhaps i missed it.

  2. #2
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    At [here], see jumper block J18.

    J18 makes sense on a type 1 motherboard because there was a model that was supplied with only bank 0 populated, i.e. 256 KB. J18 allowed the owner to choose the method of increasing that conventional memory: by populating the second bank, or by adding a RAM (conventional memory) card that is configured to start at address 256K.

    On motherboards of type 2 and 3, changing the J18 jumper to the '256K' position disables half of the motherboard RAM. The only reason that I can think of for doing that is to temporarily test out a RAM card that is configured to start at address 256K.

  3. #3

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    Quote Originally Posted by modem7 View Post
    The only reason that I can think of for doing that is to temporarily test out a RAM card that is configured to start at address 256K.
    I don’t know if it applies here, or if it’s even really true, but the AST Rampage 286 manual suggests a performance boost in expanded memory applications if the card is configured to back fill more conventional memory.

  4. #4

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    Quote Originally Posted by jafir View Post
    I don’t know if it applies here, or if it’s even really true, but the AST Rampage 286 manual suggests a performance boost in expanded memory applications if the card is configured to back fill more conventional memory.
    That's true if you're multitasking with desqview for sure. Other EMS applications I doubt it matters a whole lot

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    Quote Originally Posted by maxtherabbit View Post
    That's true if you're multitasking with desqview for sure. Other EMS applications I doubt it matters a whole lot
    Windows 2.x also needed backfilling in order to run multiple larger Windows applications at the same time especially if the applications are hooked together through DDE.

  6. #6

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    Thanks for the responses. The J18 jumper had me very confused on the Type 2/3.

    BTW modem7 what is: https://ibm.retropc.se/ ? Which one is current, that or minuszerodegrees.net?

  7. #7
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    Quote Originally Posted by mR_Slug View Post
    BTW modem7 what is: https://ibm.retropc.se/ ?
    It is someone's very out-of-date copy of minuszerodegrees.net

  8. #8

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    Is there anything in the technical manual about it? Maybe to do 256k on the board you need to use those piggybacked chips like on the type 1 boards.
    "Will the Highways on the internets become more few?"

    V'Ger XT

  9. #9
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    Quote Originally Posted by Anonymous Coward View Post
    Maybe to do 256k on the board you need to use those piggybacked chips like on the type 1 boards.
    That will not work due to differing pinouts. For example, the 41128 type chip (128 Kbit, comprising of two piggybacked chips) requires two RAS signals, but the later 5170 motherboard, being designed for a 41256 type chip, only generates one RAS signal for each chip.

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