On 04/24/2017 06:51 AM, dwight via cctalk wrote: That may be true for some systems, but for the NEC 765-based controllers found in PCs, the format operation always starts at the index (and ends there too). What isn't dependent on the index is the sector ordering; it's not at all uncommon to see a cylinder- and track- skew factor built in, such that cylinder 0, side 0 starts with sector numbering 1,2,3...18; cylinder 0, side 1 starts as 4,5,6...18,1,2,3 and so on. It avoids a lost rev when moving from track to track. Similarly, when reading, if the IDAM for a desired sector isn't seen after 2 index pulses, the 765 calls it a "not found". There are index-ignorant controllers out there, but the PC isn't one of those. My guess on the symptoms described is a scratch or spill. Sometimes these floppies can be brought back by a simple cleaning of the cookie. --Chuck

On 04/24/2017 02:40 PM, Terry Stewart wrote: If this were an 8" or 5.25" disk,I'd recommend that you try a few different drive makes. There were substantial differences in technology back then (often resulting in lawsuits for infringement). For example, a Tandon 5.25" drive tends to use heavier loading and "iron" the disk more than, say, a Mitsubishi one, which used a gimbaled head and much lower loading. Basically the idea was a tradeoff between "following" the disk waves or flattening them out. But for 3.5" drives, I don't have a clue--perhaps coating with some cyclomethicone might result in some surface-tension type adhesion and make the floppy easier to read. --Chuck