If your USB drive really doesn’t support DD disks, a nicer option for file-transfer might be a null-modem cable and LapLink or InterSrv on DOS 6. You can use DD disks as HD by drilling an extra hole but then you’re taking your chances with the magnetic support. An HD disk can be formatted as a DD in a HD drive, but as mentioned previously will be unreliable in a DD drive an HD disk formatted as a DD in a DD drive will work fine. An HD drive can theoretically operate in both modes (and will do so automatically with a DD disk). A DD disk will always end up formatted in double-density, and a DD drive will always format in double-density. Note that the holes in disks’ cases don’t determine the formats one-for-one. All is not lost though: you should format your disks in the Tandy’s drive (when you get it), and check whether your USB drive can then read and write the disks (but keep some disks aside that will only ever be written to using the Tandy’s drive). High-density and double-density disks use magnetic media with different coercivity, requiring different field strengths to write data a double-density drive can’t reliably format or alter a disk that’s been written to by a high-density drive. However since your intention is to use these disks to transfer files to and from a computer with a double-density drive, this approach is likely to be unreliable anyway. If you have a Linux system handy, you can determine your drives’ capabilities by querying it with ufiformat -i. To see what it does - USB drives control formatting themselves, so this should do the right thing if it supports double-density disks. It is still worth trying a plain format a: There are some USB drives which support double-density disks and formats, but as you suspect, not all of them. Invalid media or Track 0 bad - disk unusable. On Stephen Kitt's suggestion, I tried a standard 'format a:' but it didn't work. But it was highly rated on Amazon and some people even said they used this exact drive to format 720K. Is this possible or am I going to have to do something else? I plan on swapping my Tandy 1000 EX's 5.25' drive with a 3.5' version and I'd like to transfer images over that way (sneaker-net). It's also the disk that only has the one hole. The disk I'm using should be good but I cannot completely confirm. Just like the message said, the format failed. When I did that, here is what I got: format a: /f:720

One instance said to use the following command at the DOS prompt: format a: /f:720 Even with Windows 10 (which is what I'm using). But then I read several posts online where people say they have done it. I've read many times that USB floppy drives will not format (or read/write) 720K disks.

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