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Thread: Zenith Z-171 - memory question

  1. #1

    Default Zenith Z-171 - memory question

    My Z-171, loaded with 640k, seems to report that the upper 24k is missing. This continues to be reported as I remove ram from 640 to 576 to 512 to 256kB. Always top 24k is "missing".

    Checkit reports it as reserved, chis is the same notation as addresses above 640kB.
    If I ask Checkit to test from 616k to 640k, it seems to report that this memory is fine. Strange!

    I suspect the RAM is there and working, in addresses 09A000h to 09FFFFh.

    Would it be believable that the Zenith BIOS steals some system RAM for other uses? OR - do I have an actual hardware problem somewhere?

    thanks,

  2. #2

    Default

    Just to finish this thread. Z171 bios mis-reports memory size at 40:13 in BDA. For 640k, values are supposed to be 02h 80h. Z171 reports 02h 68h. That's off by 24k.
    Quick fix in my case-
    * since I am using the XT-CF card, and I have to patch the BIOS anyways to run in Z-171, I can apply a patch there to correct the reported memory
    * a single line of code that writes the value 080h to location 0040:0013 seems to do the trick.
    * DOS boots and correctly reports RAM amount.

    A better patch would be to read back the provisioned amount by Z171 BIOS, add 24d to it, and write it back.

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