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Re: Altairs and Disk Drives

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  • mfeberhard
    Speaking of a Rosetta Stone PC for disk formats - I have built such a system using an older Dell PC running XP and DOS. I used Dbit s FDADAP board to connect
    Message 1 of 34 , Nov 14, 2011
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      Speaking of a "Rosetta Stone" PC for disk formats -

      I have built such a system using an older Dell PC running XP and DOS. I used Dbit's FDADAP board to connect a Shugart SA851 8" floppy, as well as a 360K 5.25" floppy connected directly to the Dell.

      I use Dave Dunfield's "Image Disk" utility to read and create .IMD archives (which is a decent archival format). I have found a lot of Cromemco software in this format.

      I also use Sydex's 22DISK.COM to read and write CP/M disks directly from the PC. Works great. I use their 22NICE CP/M emulator to write CP/M code on my PC (assembling the code using Digital Research's ASM or MAC), then transfer it onto a floppy and onto the CP/M machine.

      However... this system does not work for hard-sectored disks, such as Altair disks. The disk controllers in PCs have no idea what to do with a hard-sectored disk.

      Also: disks created with a controller board using the WD1772 are often problematic on other controllers (including PCs), because the 177X does not quite follow the IBM 3740 floppy format. For this reason, I vastly prefer disk controllers that use the later WD179X controllers, which got the format right. For example, I like the CCS 2422 controller - works great.

      I am told that the Catweasel board (funky PC disk controller) can even handle hard-sectored disks, and I recently bought one. But I have not had time to figure out how to use it.


      --- In altaircomputerclub@yahoogroups.com, "Stephen L" <shlafferty@...> wrote:
      > > 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.
      > --- Those Foley mainframes with their integrated drives are interesting.
      > I take it that they used MITS DOS? I keep hearing that some old 360K
      > drives may work with some controllers. Herb Johnson has mentioned using
      > Versafloppy-II controllers. Of course, it's all about mating the
      > controller with the particular OS. I get the impression that I'm going
      > to end up writing 8080 code again, after 35-years :) It also looks like
      > getting a custom 1702A eprom burned will be in the picture.
      > > 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.
      > --- There is no doubt that solving the floppy controller/driver problem
      > was one of the tougher tasks that the microcomputer companies faced,
      > back in the day. iCOM was indeed a pioneer. Offering a 5-1/4-inch floppy
      > system for the S100 bus back in 1977 was pretty innovative.
      > > Reading and writing an a PC will be a challenge, especially the FDOS
      > > format.
      > --- Yes indeed. My hopes were buoyed by seeing evidence of the XenoCopy
      > software, though I guess it may have disappeared. Scanning their list of
      > formats though, doesn't turn up much for names like MITS, iCOM and
      > NorthStar. Also stumbled across OmniDisk, which claims to be "capable of
      > reading, writing and formatting any physical format to the limit of the
      > hardware, and it will recognize (and a put a name to) some formats seen
      > before."
      > >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.
      > --- That is an interesting option. I seem to remember something about an
      > adapter like that--who provides it?
      > > 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.
      > --- Yes---Please, if anyone has documentation on the iCOM microfloppy
      > controller or software for it, I would be very grateful. My unit is
      > missing one of the small chips and I can't even find out what that is
      > supposed to be. If anyone has the controller, I would really appreciate
      > knowing what chip is in U12.
      > > 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.
      > --- That is a worthy goal. Achieving it would do a lot to get these
      > systems running again. After looking around, I'm getting the impression
      > that having actual floppy hardware and software currently working is
      > somewhat uncommon. When I asked one knowledgeable seller for a
      > controller and floppy solution, he could not offer offer one, saying
      > that controllers and floppies "aren't plug and play". I see a lot of
      > people selling boards and drives but haven't found a source for a
      > working combo. Of course, software is in the mix, too.
      > Part of my interest in finding PC software which could use a 360K drive
      > to read/write multiple standards would be that it could become a Rosetta
      > Stone, allowing hobbyists to exchange software.
      > 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
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        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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