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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?

    #2
    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.

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      #3
      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

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        #4
        I thought on Victor Sirius, but there the floppys were double sided. https://en.wikipedia.org/wiki/Sirius_Systems_Technology
        <album>

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          #5
          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.

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            #6
            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.

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              #7
              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...

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                #8
                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.

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                  #9
                  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.)

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                    #10
                    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.

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                      #11
                      I never heared about single sided Victor disks. And usually they are not MFM coded, but GCR.
                      <album>

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                        #12
                        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.

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