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Anyone know of this system?

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    Anyone know of this system?

    I've got some 5.25" disks here from some system running MS-DOS 2.x. The odd thing is that they're 96 tpi single-sided and high (500KHz) density. I've not decoded them yet, but they're definitely MFM, based on the pulse histogram. Based on a printed directory listing, the disks hold somewhere around 700KB each.

    Does this ring any bells with anyone?

    Originally posted by Chuck(G) View Post
    I've got some 5.25" disks here from some system running MS-DOS 2.x. The odd thing is that they're 96 tpi single-sided and high (500KHz) density. I've not decoded them yet, but they're definitely MFM, based on the pulse histogram. Based on a printed directory listing, the disks hold somewhere around 700KB each.

    Does this ring any bells with anyone?
    Single sided MS-DOS 2.X at 96 tpi sounds like Dec Rainbow 100 (RX-50), but they would be quad density (400k per side) not high density.


      The Epson QX-16 ran a non-IBM MSDOS in I believe releases in 2.2 and 3.3. But I'm not sure if SS or DS quad density on the original diskettes, since I seldom use the original diskettes. I fact now that I think about it, I don't even have a complete set of original DOS diskettes for the QX-16.
      Crazy old guy with a basement full of Pentium 1 laptops and parts


        I thought on Victor Sirius, but there the floppys were double sided.


          The media are definitely single-sided. What's making recovery difficult is that double-density media were used, so the peaks are more than a bit "blurry". It's not normal MFM either. No later than 1985.


            I vaguely remember that something used 720K single sided disks but the only reference I can find is a mistaken comment about the Tandy 2000. It is strange that there does not seem to be an announcement in Infoworld; a press release of someone using the Micropolis high density single sided 5.25" drive seems like a source for a filler article.


              Didn't the Sanyo MBC-500 PCs have an option for SSDD 96 tpi? Seems to me that it did. But these are high-density and not standard MFM (I'll get those details figured out later).
              I'd thought about the Victor 9000, but those were double-sided and GCR.
              I wonder if this isn't some 8" system that was hooked to a 5.25" drive...


                Perhaps a Xerox 8/16 Professional Computer? It ran MS-DOS 2.x, and supported 8" and 5.25" floppy drives. Its single-sided, double-density 8" format was 1024 bytes per sector, 8 sectors per track, and 77 tracks, for a capacity of 616K. Maybe someone got it to do this format on a 5.25" drive.


                  I'll know more in a couple of days, but right now, no standard ID headers at all. So that leaves out any of the "commodity" FDCs (WD 17xx, 37xx, NEC 765, etc.)


                    I finally had time to dig into the flux data. It's a single-sided Sirius/Victor 9000 format. What threw off my histograms was the "gap" before the VCO sync leadin--on my samples, it was pure garbage. I confess to never having run into single-sided Vicky stuff before.

                    Time to sit down and write a decoder. Should be interesting, as these disks were repurposed from other systems before they were written in 1985 and I suspect that time has not been good to them. Since single-sided, I only have to deal with 8 speed zones.


                      I never heared about single sided Victor disks. And usually they are not MFM coded, but GCR.


                        The histograms are a bit blurry, due to the CLV zoning and the lead-in sync patterns. So yes, they look like MFM until you get down to the actual bit-twiddling.

                        Judging from Vicky owners' experience with the old floppies, retrieval is a bit dicey in any case. With re-purposed media, it's going to be interesting.
                        Last edited by Chuck(G); Today, 08:55 AM.