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.

Direct data copy no format floppy disk