On Sat, 10 May 2014, shadoooo wrote: Nah. You can have a valid MS-DOS format, and versions of DOS and Windoze that do not support THAT format will still choke on it. Microsoft did not standardize the format of 720K until DOS 3.20. MS-DOS 2.11 (there is no PC-DOS 2.11) includes additional features added by the computer manufacturer. EVERY version of 2.11 is potentially different. The earliest 3.5" drives were single sided. The formats were not standardized. The earliest 3.5" diskettes had no shutter! Then came a manual shutter. Then a spring loaded manual shutter (slide it open, and then pinch the corner of the diskette where the arrow points when you want it to close) Then the familiar automatic shutter, although many diskettes still have that little arrow embossed on them! There were once 3.5" diskettes with 40 tracks per side 67.5tpi, although Epson Geneva PX-8 is the only one of those that you are likely to run into. Almost everybody else standardized on 135tpi (80 tracks per side) Then came double sided 3.5". Those formats were not standardized, although SOME companies had inside information, or made lucky guesses about the exact structure of the later "standardized" 3.5" format. Some, such as Gavilan, had more than one double sided 3.5" format. Well, Gavilan started off with 3", then single sided 3.5", and then the company went under about the time of their double sided. What version of DOS are you running on your PC? If you have to run Windoze, at least go to a CMD window! Otherwise, Windoze will take the errors that it encounters, HIDE the details about what is actually wrong, and replace that with "You are screwed. OK?" At least in the command line window, you can differentiate between a parity error, a sector not found (there are sectors! just not the right one), and a unformatted or wrong density disk. If DOS goes through its short list of known problems without finding the specific one, it will say "General Failure" (referring to the leadership in Nam?) DOS can determine WHICH disk format a given disk is either by an arbitrary special byte as the first byte in the File Alloscation Table, OR by a table of disk format parameters in the boot sector. Which of those two methods would YOU think would make the most sense? So, therefore, MS-DOS supports a very limited number of formats, and guesses which one of those it is, rather than an unlimited selection based on the parameters. That seems likely. or disk controller circuitry. MS-DOS 2.11 (and a few others) would sometimes give extraneous track 0 errors when formatting, if the DMA buffer straddled a 64K boundary. If it will read and write, but fails track 0 in format, then adding or subtracting a device driver (ANY device driver) could be used to change wehere the buffer ended up. or disk controller. yes Do you have access to one of the external 5.25" drives? -- Grumpy Ol' Fred cisin at xenosoft.com