Problem reading CP/M floppy on a PC

On 14 May 2007 at 23:50, John S wrote: I hadn't realized that there was a norm for CP/M floppies. You know, the "recommended" 512-byte sector "packing" in the uPD765 literature is 8 sectors--and indeed, early PC-DOS used just that. It's entirely possible to fit 10x512 sectors per track using a 765- type controller, though it's much easier if the IAM is left off and the space gained used to expand the inter-sector gaps (you can do this with a uPD 2765-type controller or any of the WD 17xx/27xx controllers. Nope, the 1771 is restricted to FM only. Maybe a 179x or 1770/1772/1773 though. It's entirely possible that the drive used to create the diskettes was somewhat out of alignment. You may have to "unalign" a drive to successfully read these. This is more common than you might think. You didn't mention if you were using a 48tpi ("360K") drive to read these or trying to get by on a 96tpi ("720K" or "1.2MB) drive. The former will usually produce better results. If the first sector on the track is consistently missing (not always the lowest-numbered; some systems skew the tracks for better performance), you might be able to recover it by slowing the drive a bit to allow the first sector IDAM to move outside of the 765 "blind spot" at the beginning of a track (although the 765 formats a track with an IAM at the start, it never reads it). Clean heads, as Dwight's mentioned, also count for a lot. Cheers, Chuck