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  • 8550-021 and 8550z ponderings

    From Louis Ohland@[email protected] to comp.sys.ibm.ps2.hardware on Mon Feb 9 16:07:58 2026
    From Newsgroup: comp.sys.ibm.ps2.hardware

    8550-021 memory, two 30-pin SIMMs, 512Kx9 at 120nS
    8550z memoir, 1MB -OR- 2MB 85nS 72-pin SIMMs
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  • From Louis Ohland@[email protected] to comp.sys.ibm.ps2.hardware on Mon Feb 9 16:21:45 2026
    From Newsgroup: comp.sys.ibm.ps2.hardware

    So... how does the 8550-021 configure memory? You can have one -OR- two
    512kx9 30-pin SIMMs. But does the -021 differ between one or two 512Kx9
    SIMMs?

    Louis Ohland wrote:
    8550-021 memory, two 30-pin SIMMs, 512Kx9 at 120nS
    8550z memoir, 1MB -OR- 2MB 85nS 72-pin SIMMs
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  • From Peter H. Wendt@[email protected] to comp.sys.ibm.ps2.hardware on Tue Feb 10 00:26:29 2026
    From Newsgroup: comp.sys.ibm.ps2.hardware

    Hi Louis !

    So... how does the 8550-021 configure memory? You can have one -OR- two 512kx9 30-pin SIMMs. But does the -021 differ between one or two 512Kx9 SIMMs?

    The 30-pin modules have 2 presence detect pins at module pins 24 and 25.
    These signal a) presence and b) size (256, 512) towards the board. Can't remember if the Type 1 systemboard of the -021 is even capable to run on
    a single module, since the memory databus is 16 bit which requires two modules. Officially the 256K modules / 150ns were not supported even
    though available for other purposes. I think they used them on some communication adapters. Other than the Mod. 30-286 the 50-021 doesn't
    support the 1 and 2M 30-pin modules AFAIR.
    --
    Very friendly greetings from Peter in Germany
    http://www.mcamafia.de/
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