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Thread: Whats the bare minimun to boot DOS?

  1. #11
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    Fwiw, the Tandy 2000, which loaded most of it's bios from disk, supported 768k ram. With hardware and software tweaks, it could use 896k. Clearly it wasn't IBM compatible, except at the bios or dos function call level.

    An interesting board, but also not ibm compatible, was the Radio Electronics RE Robot Brain (80188 based). I have some firmware files. It uses a serial terminal for output also. I have to e-mail the guy who built one (the whole robot). I hope he's still available to chat.

  2. #12
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    The Durango Poppy used serial I/O and an 80186 to support MSDOS (still have the I/O source), but as far as I know, never got beyond MSDOS 2.1.

  3. #13
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    Written in assembler? Can I have a copy?

  4. #14
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    I don't know if I have an electronic copy or not--my copy is paper--fan-fold 14" greenbar and lots of it. I'll see what I can find. You did catch my post about the MS guide to DOS 2.0 OEMers, right?

  5. #15

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    Quote Originally Posted by 1ST1 View Post
    That would be a lot! Early PCs came up with not more than 128 kB.
    Oops yes that was a typo, I meant 256kB. This forum won't allow me to correct it. I will need to be more careful if and when I say something else.
    I wonder if 64kB would work with Dos 1.0 (or is it PCDOS?).

    And, when quoting, it doesn't include the original quote, leaving this one out of context. Grrr.

  6. #16
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    PC-DOS 1.0 should boot with a mere 32 kB installed.

  7. #17
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    SBC-188 can boot MS-DOS 6.22. Its BIOS actually implements INT 10h and INT 16h emulation using serial port.
    What did it take:
    - IBM compatible BIOS. Note that even the entry point addresses are important. DOS calls some BIOS services using CALL <entry_point> instead of INT.
    - Other than obvious INT 10h, INT 13h, and INT 16h, you'll need to implement INT 11h, INT 12h, and stubs for INT 14h, and INT 17h.
    - I think I spent a couple of evenings debugging BIOS and DOS interactions to make it boot...

    As others have mentioned, this will boot DOS, and run some console-based DOS utilities, but way too many programs access the hardware directly, and especially display memory.

  8. #18
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    Well, if you provide RAM in the display area and limit the display ID to MDA, one could interrupt whenever the display area is written. I tried that back in the 5150 days, replacing an MDA with some memory and some software. It worked back then.

  9. #19

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    Quote Originally Posted by sergey View Post
    As others have mentioned, this will boot DOS, and run some console-based DOS utilities, but way too many programs access the hardware directly, and especially display memory.
    This!

    On non-standard systems, some with more than 640k conventional DOS memory, things can get really interesting if programs just assume video memory to be present in the A or B segment.

  10. #20

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    Quote Originally Posted by sergey View Post
    IBM compatible BIOS. Note that even the entry point addresses are important. DOS calls some BIOS services using CALL <entry_point> instead of INT.
    Do you know which BIOS services are called by address instead of INT? I have an 80186-based system running MS-DOS 3.10, and eventually I'd like to get a newer version of DOS working on it. But if the BIOS is strictly incompatible, this won't be possible.

    I noticed that MS-DOS 6 will talk to a PIC-style interrupt controller in its early code, but I don't know if one is strictly required afterwards.

    FreeDOS will definitely not boot with 256 KB or memory; its startup code is relocated at a higher address. I don't remember if 384 KB of RAM are sufficient.

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