Re: Altairs and Disk Drives
- 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 email@example.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
> >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
> > 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
> > 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.
- 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 firstname.lastname@example.org, "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.
> Herb Johnson