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Thread: Disabling DOS/Deskmate-in-ROM on a Tandy 1000 HX: Close! But... ideas?

  1. #11
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    Quote Originally Posted by soviet9922 View Post
    Very cool and you got a lot of free ram there .
    I've made it even a little bit crazier; per this thread I've written a little "enabler" that lets me use the EMS page frame as an additional 64K of UMBs just in case there's some situation where maximum base RAM with a ton of drivers installed is more useful than EMS. I'm going to try testing that out with an NFS file sharing stack ASAP. (Said stack takes almost 60k of RAM.)

    Practically speaking why anyone needs all this in an HX, well... "because you can" is clearly the only valid answer.
    Last edited by Eudimorphodon; July 30th, 2020 at 01:58 PM.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

  2. #12
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    Having some extra UMBs space in the tandy HX and SL is something very handy indeed for tandy owners.
    Hope your project get to "mass production".

    Do you use or plan to use only dip packages or you will use smds ?.

  3. #13
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    Quote Originally Posted by soviet9922 View Post
    Having some extra UMBs space in the tandy HX and SL is something very handy indeed for tandy owners.
    Hope your project get to "mass production".
    I don't have an SL, alas, but I do wonder if a similar technique would be possible to override its ROM DOS. I have this feeling it might be somewhat less trivial, unfortunately. With the 8086 there are bus size issues, and I assume the ROM is 16 bits wide in those machines? (I honestly don't know off the top of my head.)

    What I really need to do is sign up someone to help me figure out if it's possible to kitbash the TX BIOS so the "768k mode" can be backported to the EX/HX/SX. Since installing the VGA card I've been running some benchmark programs to satisfy my curiosity about how the "Big Blue" RAM performs when it's not doing video refresh, and the long and short of it is these machines take a pretty large performance hit whether you have a VGA card installed or not because that part of RAM that's backfilled with video memory runs at an effective 4.77mhz-ish thanks to wait states. If we could override the ROMs in the EX/HX/SX with a hacked version that would test for expansion memory up to 640k and switch Big Blue to the "Video Only" mode like the TX then it would be a significant speed boost for large memory applications. (I have confirmed with manual experimentation that the EX/HX support the necessary mode, just need the BIOS support for it.)

    Granted whether it'd be worth anyone's time is a totally valid question.

    Do you use or plan to use only dip packages or you will use smds ?.
    My board is all through hole:

    expansionhack.jpg

    I've been thinking of trying to do one with surface-mount RAM chips, since 3x512k is the maximum that's feasible in the space available with all the other features on the board; they make a suitable 2MB RAM chip and in theory the EMS page registers layout can support up to 4MB. Of course I haven't really come up with a good use for the 1MB I have.
    My Retro-computing YouTube Channel (updates... eventually?): Paleozoic PCs

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