Loading ...
Sorry, an error occurred while loading the content.

Re: Altairs and Disk Drives

Expand Messages
  • W Tom
    My focus on 8-inch drives is changing due to 8800b-sm and 8800b-dm mainframes. I need 5.25-in drives and controllers that are affordable and available for
    Message 1 of 34 , Nov 13, 2011
    • 0 Attachment
      My focus on 8-inch drives is changing due to 8800b-sm and 8800b-dm
      mainframes. I need 5.25-in drives and controllers that are affordable
      and available for multiple mainframes.

      I like to hear of people restoring iCOM equipment. iCOM was a pioneer
      too. iCOM engineers made contributions to Altair design like the 3202
      drive cabinet. iCOM programmers helped repair Altair accounting
      software.

      >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 :)

      Reading and writing an a PC will be a challenge, especially the FDOS
      format. Part of my interest in the Teac FD-55 GFR drives is that
      adaptors are available to make then look like 8-inch drives. The 8-inch
      SSSD CP/M format can become a new 5.25-inch standard.

      Good luck with the Microfloppy. I hope someone comes up with a manual.
      Hopefully someone with a have a dual-drive Microfloppy system to copy
      boot disks. Perhaps someone has a CP/M BIOS configured for a Microfloppy
      or close enough to modify. At this point I'm not so concerned with what
      was common in the past. I want mainframes to have any drives that are
      affordable and have media that can be read by other Altair owners.

      What drives and format are working in an Altair in 2011? So far, I can
      only exchange software in MITS Format or using modem protocols. Does
      anyone in the group have an iCOM 3712 or 3812 running FDOS or CP/M? Does
      everyone with working MITS drives have boot disks?

      Tom S.


      Tom S.

      --- In altaircomputerclub@yahoogroups.com, "Stephen L" <shlafferty@...>
      wrote:
      >
      > 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
      • 0 Attachment
        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
        >
      Your message has been successfully submitted and would be delivered to recipients shortly.