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Thread: 3274 21C Worth Picking Up?

  1. #31
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    Hmmm, the first three peaks look like MFM to me--the remainder resemble nothing more than harmonics. The shape of the histogram would certainly imply that.

    Pin 3 is probably INUSE--very common on many drives.

  2. #32

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    If it was MFM wouldn't you still expect to see certain conventions like 0x4e gap bytes (the screenshot I got at least did not appear to be 4e).
    Also what would a different RLL code look like on the histogram.

  3. #33
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    So, you've got the system; what is being used as a controller chip?

    I don't think it's (2,7) RLL either--with RLL, the maximum frequency doesn't change; the spacing between transitions is more critical, however--i.e., most RLL encoding in excess of MFM is not very tolerant of jitter, which is why you don't see it in floppy disk systems (the coating thickness and frictional effects don't make for a suitable medium). Even at that, (2,7) would only give you 50% more data than a normal HD MFM floppy, if it indeed were practical.

    GCR is much preferred in that case--but then, you'd see roughly equal peaks (usually 4 or 5).

    Or so I think.

    What are you using to read the floppy? (you might have mentioned that and I missed it). When you develop the tracks using something like Kyread, what do you see under the microscope?

  4. #34
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    Quote Originally Posted by Chuck(G) View Post
    So, you've got the system; what is being used as a controller chip?
    Interesting question Chuck. On the rack mount model I have there are three Intel chips 8055 family chips near the front panel board. The floppy/disk controller chips appear to be Toshiba but I can't find any data sheets.
    They say things like T3A33A/39f8850 37x3718/t4941 66x2711/t5851. Seeing as Toshiba invented this "Extended Density" with vertical recording does any one have any pointers to a Toshiba FDC that supports it? I couldn't find any but perhaps my google foo has failed.
    Dave
    G4UGM

    Looking for Analog Computers, Drum Plotters, and Graphics Terminals

  5. #35

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    Quote Originally Posted by Chuck(G) View Post
    What are you using to read the floppy? (you might have mentioned that and I missed it). When you develop the tracks using something like Kyread, what do you see under the microscope?
    I first tried using my Pentium II machine which has a controller capable of 1Mbps and the HxC software, but that could only read the first cylinder.
    After that I used a rpi and this project since that's what I had around, https://github.com/picosonic/bbc-fdc.

  6. #36
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    There's a lot of unverified information about the 2.4 (3.2 raw) format that could be answered with a few simple tests.

    The reason I asked about the developer is that some people say that the EHD disks are 192 tpi, which wouldn't be unreasonable. That would at least allow them to perform as double-sized 1.2MB floppies. But again, that's just a rumor. The YE Data/C Itoh YD801 drives (not the Hitachi drives used by IBM) claim compatibility with 360/12 media, which again has me wondering if it's simply not a matter of doubling the number of tracks (the Drivetec drives did that and went even denser). The other issue is control signals--it would be interesting to monitor the state of, say pins 2 and 4 on real equipment to see any unusual signals being asserted by the host.

    At this point, I'd be unwilling to chalk matters up to some exotic modulation scheme.

  7. #37

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    Quote Originally Posted by Chuck(G) View Post
    The other issue is control signals--it would be interesting to monitor the state of, say pins 2 and 4 on real equipment to see any unusual signals being asserted by the host.
    All of the even pins on the hitachi drive I have are clearly grounded, a quick visual inspection reveals as much.

  8. #38
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    So, it's an "upside down" drive? (on a standard floppy drive, it's the odd pins that are grounded). Strange, that.

  9. #39

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    Oh sorry, I mixed up my numbers.
    2 is an input to the drive. 4 is an output and behaves like I described earlier, probably INUSE.

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