TG43 signal and the Nec 765 (Jules Richardson)

The TG43 signal has NOTHING to do with pre-compensation. The original IBM specification for single density (128 byte per sector, 26 sector per track, 77 tracks) floppies has an option to change the write current on the drive head for the more densely packed sectors on the interior of the disk. because of the constant angular velocity (360 rpm to be exact) the interior tracks were more dense than the outer ones. To prevent the bits from blasting into each other they (IBM) reduced the write current on the inside (greater than 43, thus TG43) of the disk. This was purely a drive option. Some later drives had more smarts and could count track position on their own, and didn't need the signal. Precompensation was NOT used on single density 8 inch drives. When things changed to double density drives (MFM encoding) precompensation was necessary when too many transitions were next to each other. The floppy formatter chip usually did this internally, and since it had the track register, it could do it "automagically". Some did it differently, but it basically shifted the bits a bit to one side or the other to "compensate" for bit crowding. ____________________________________________________ Start your day with Yahoo! - make it your home page http://www.yahoo.com/r/hs