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I am using a USB connected "Sabrent FD-05PUB" 3.5″ floppy drive to read data using Windows 10 computer. It shows in Device Manager as "TEAC USB UF000x USB Device". The 1440 KiB disks read just fine. All 720 KiB floppies error with:

A:\ is not accessible

The disk media is not recognized. It may not be formatted.

Any ideas?

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    Doesn't seem like a question for the retrocomputing forum - the only retro part is the "half-density" medium. Computer and drive are modern. Is there any specification that says the drive even supports 720kB format? May 19, 2020 at 23:27
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    I'd say as well it's not RC.SE related. The basic issue revolves around the fact that 720K Disks are DD while 1.44 are HD. This means different timing, even if MFM is used for both. Media, Drive and Driver need to be aware of that and supporting it. So check your OS as well as the drive if this combination is capable to handle 720K. Also, check the disk used - DD Disk got only one hole in the corner.
    – Raffzahn
    May 20, 2020 at 0:02
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    I can see why someone would consider reading 720K disks "retrocomputing", though. Might be something for the superuser stack exchange. May 20, 2020 at 4:29
  • just a silly question but what file system are the floppies formatted with?
    – Spektre
    May 20, 2020 at 8:08
  • Ah, "TEAC". That's a blast from the past ...
    – davidbak
    Feb 25 at 17:40

1 Answer 1

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Some USB floppy drives don't support double-density floppy disks (as opposed to the newer high-density disks that are usually formatted to 1440KB). I think it's usually a limitation of the controller chip interfacing between USB and the drive itself.

You should try using a different drive, and look specifically for reviews of its performance on double-density disks.

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  • In the good old times we could even tune drives to physically store 800Kb in DD disks and 1800Kb in HD. See 2M from Ciriaco García de Celis. I suppose now everything is done with integrated software and if that software is not smart enough there is probably nothing to do.
    – arauzo
    May 20, 2020 at 15:02

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