DD/SD floppy drive?

Hardware
21

As mentioned above, it also depends on the OS. I’d recommend trying with WinXP from inside a VM.

And it could be about the media descriptor byte of the boot sector missing or not matching anything supported by the BIOS (which may be worked around). Compare:
https://support.microsoft.com/en-us/topic/floppy-disk-is-not-accessible-not-formatted-or-not-recognized-by-windows-17c4e169-ed8d-2d5a-aaf0-fd257b80ac3a
This should be solved by attempting to read the disk from inside an appropriate VM, as well (as this comes with its own BIOS).

22

I found it weird all HD disks had no issue reading, then all the other floppies could’nt be read
so idk

23

I dont think the bios has anything to do when floppies are read by an usb floppy device
AFAIK, mb floppy controllers were actually controlling everything happening inside the cpu/mpu-less floppy drive

if all my SD floppies cannot be read by that usb floppy drive, then it is its fault

hence my will to find a good-ole retro computer

24

There are quite a few USB floppy drives that can only handle HD disks in IBM format. They have a very crude idea of how a floppy should look. Their controller hard-codes seek positions against particular track step and head selections. They cannot understand anything but a standard 1.44 MB HD floppy.

If your USB floppy drive was made this century, it’s probably one of these. The more solid Dell or ThinkPad-branded ones tend to work with any MFM 3.5" floppy format

2 Likes
25

The drives speak a sort of SCSI protocol. The drivers on the PC end are usually the problem - paritcularly it seems on Macintosh and Windows 10 and higher. The TEAC, Tandberg and most other units support both at the device level but not in Windows 10/11 or modern MacOS.

The actual specification covers 720K DSDD (and thus SD because you just only read the right sectors), 1.2MB DSHD and 1.44Mb DSHD.

A MODE_SENSE will hand you back 1E, 93 or 94 according to the mode

1 Like
26

so in the end, I guess I’ll try not to get scam on ebay…

27

Compare from the support document linked above:

This problem occurs on disks that do not contain a media descriptor byte in the BIOS parameter block (BPB) of the boot sector. Some older preformatted floppy disks do not contain a media descriptor byte. Older product disks may also not have the media descriptor byte.

The media descriptor indicates the type of medium currently in a drive. With MS-DOS and Windows 95, you do not have to set the media descriptor byte. Therefore this problem does not occur with these older operating systems.

Meaning, if you were generally using preformatted disks under DOS or Win95, this may be an issue.

28

would mean I never formatted any of these floppies. which I doubt