On Tue, Oct 13, 2009 at 7:48 PM, Jinx wrote: > I took the 2GB card back, [...] happy to swap it for a 4GB, ... > Well, now you've gone and ended the adventure, and we were just getting started. Party pooper. Well, at least you've kicked off a physics discussion. I feel as though I am posting off-topic if I talk about storage media :) On Mon, Oct 12, 2009 at 2:56 PM, Tamas Rudnai wrote: > > As far as I remember the problem with diskettes was that they have stored > the index marks magnetically on the disk (I mean the IBM disk drive, other > ones were using the index hole Almost every diskette technology used magnetically recorded index marks. The drives/media that had mechanical index hardware was just used it to time where they'd start writing the track during a format run. And they'd use it to determine if the disk was spinning. > There was an index mark for the first sector and then for each > additional sectors, all with synchronization data and some information > about > the sector and cylinder number. When you formatted the disk you had to > clear > not just the data but the index marks as well to make sure the diskette > worked ok. > The format procedure wrote an entire track, with all of the things you mentioned above (plus some "gaps"). And so it was possible to format a diskette that had no magnetic transitions at all (a truly "blank" disk). The problems we would sometimes run into was if there was something that looked like a parameter block in sector 0, the system would read that and possibly believe what it saw. Then it might decide it could not format "that" kind of disk. If you degaussed it, then the system would just shrug, then go ahead and format it. Barry -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist