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Re: Altairs and Disk Drives

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  • Stephen L
    Hi Tom, Thank you for the nice message. Yes, the boot prom on the controller has a label which is partially obscured, but I can make out ?DOS M on it. I
    Message 1 of 34 , Nov 13, 2011
      Hi Tom,

      Thank you for the nice message. Yes, the boot prom on the controller has a label which is partially obscured, but I can make out "?DOS M" on it. I assume that is FDOS-M, which I guess was another version of FDOS-III.

      I did find one person who has the FDOS boot disk but he understandably is reluctant to loan it out remotely and doesn't have a way to read it. Have searched the Web but haven't found an image of it yet. If I do manage to find and read a diskette, I'm certainly going to put it up on the Web!

      I understand about your focus on 8-inch drives. Those were surely more common on these machines. My interest in the Microfloppy arises out of having the card, the hope that somewhat newer 360K drives might work with it and the fact that 5-1/4 media have some hope of being read/written by special software running on a PC. (Lotta "hopes" in there :)

      Steve L.
    • dsroelov
      regarding herb s post below, i remember the days of writing disk drivers for my 8800B. it still had a 2MHz 8080 and it had the same old MITS disk controller.
      Message 34 of 34 , Jan 4, 2012
        regarding herb's post below, i remember the days of writing disk drivers for my 8800B. it still had a 2MHz 8080 and it had the same old MITS disk controller. timing out the read loop, i think it took 31.5 microseconds to run the loop, and a new byte came from the controller every 32 microseconds. you snooze, you lose.

        i also remember some crazy read code that came from extended basic, or DOS, or CP/M, or somewhere, that read two bytes at a time from the controller. it did not check the "ready" flag for every byte, it just checked the flag, read a byte, added a couple of NOP's for timing, then it just read another byte. after the second byte, it looped back to the beginning and checked the flag again. dangerous code. a stray microsecond here or there, and you were screwed.

        in any case, unless your controller has at least a one sector read buffer (whatever that sector size might be), single density is probably as good as you'll get on a 2MHz system with the original MITS disk controller.


        --- In altaircomputerclub@yahoogroups.com, "thinkpast" <hjohnson@...> wrote:
        >

        >
        > The core problem of use, relevant to MITS 8080 owners, is this. How can a 2Mhz CPU, keep up with all the data in real time from the floppy diskette, through the read head? Since double-density formats have twice the data, that increases the difficulty. Most say it's simply not possible to manage double-density with a 2MHZ 8080.

        >
        > Regards,
        > Herb Johnson
        > retrotechnology.com
        >
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