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Thread: TRS-80 Model II acquired.

  1. #21
    Join Date
    Jan 2012
    Connecticut, USA


    So what are some methods for writing to 8" disks to create new Model II disks? I have 8" floppies. I own a kryoflux, is there anything I can do to make my own disks?

  2. #22


    Quote Originally Posted by bladamson View Post
    I need to study the schematics a little more closely, I think. I just read something on the web that says the Model 16/6000 maxed out at 1mb of RAM. But I thought the M68k had a 24 bit address bus, so it ought to be able to address 16 meg. Maybe their funny ram connector thing doesn't expose all the address lines, or maybe it's a ROM thing or... I dunno.
    Hi, there! Firstly, welcome to the world of Big Tandys!

    The first 68K processors actually did have 24-bits of addressing, but only 22 were available on the Tandy CPU boards. Due to this, and due to the fact that there were some memory mapped hardware addresses near the upper end of this range, the maximum theoretical usable memory for XENIX is 7.5 MB. However, the practical limit was 3MB due to timing and stability issues. This meant you'd have a CPU board, and three 1 MB memory boards. I personally got 4MB to work on one particular system, but that was more of a fluke.

    The 1 MB limit you were reading about was for XENIX prior to version 3.2. In those prior versions although the XENIX kernel could see all memory present, the onboard MMU could only offset up to 1MB which meant stock XENIX could only use 1MB. There were third-party solutions that would, for example, use anything above 1MB for RAM swap.

    This all changed when the Tandy MMU daughter board was released. It added two more bits to the MMU, which allowed up to 4 MB of user memory. XENIX 3.2 and later knew about and programmed all three bits of an MMU extension assuming it was there. The original Tandy MMU is a very rare bird. However, some in the community have started work on a replacement based on a third-party design that uses all three bits instead of just two like the original Tandy.

    Let me know if you have any other questions!

    (yes, this was my actual email when I worked at Tandy)

  3. #23


    Quote Originally Posted by VERAULT View Post
    So what are some methods for writing to 8" disks to create new Model II disks? I have 8" floppies. I own a kryoflux, is there anything I can do to make my own disks?

  4. #24


    Sounds like getting a Xenix-compatible hard drive going will be the most challenging from a parts acquisition standpoint.

    I guess Xenix is closed source, and so we can't write device drivers for the lotech-type boards, eh?

    Sounds like the type 4 board is what I need, and an MFM hard drive emulator. Anyone want to sell me a type 4 board? Lol.

    Or hmmmmm....... If the hardware specs are all available, maybe I could make one...... I'll have to see about downloading a Tandy 6000 technical manual and poking around.
    -- Lee
    If you get super-bored, try muh crappy YouTube channel: Old Computer Fun!
    Looking to Buy/Trade For (non-working is fine): Tandy 1000 EX/HX power supply, box of 8" floppy disks, Mac IIci hard drive sled and one bottom rubber foot, Hercules card + mono monitor (preferably IBM 5151), Multisync VGA CRTs, 040 or 601 card for Mac IIci, Decent NuBus video card, Commodore PC(286+), PC-era Tandy stuff, Aesthetic Old Serial Terminals, Amiga 2000 or 3000UX

  5. #25


    For any epoxy job I would recommend WEST epoxy and fillers. Cant go wrong.

  6. #26
    Join Date
    Jan 2014
    Western North Carolina, USA


    The Tandy 6000 service manual is available on, as well as in pski's model2archive. Look in the directory
    Thus spake Tandy Xenix System III version 3.2: "Bughlt: Sckmud Shut her down Scotty, she's sucking mud again!"

  7. #27
    Join Date
    Feb 2014


    Sorry I made a mistake in this summary.

    *) Harddisk controller type 4
    *) F48, The ModelII version of the FreHD
    *) MakeVhd v. 1.7 To solve some software problems with FORMAT command

    This line should read: Harddisk controller type 4 ->>> Harddisk controller type 2


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