On 2/27/23 12:55, r.stricklin via cctalk wrote: > >> On Feb 27, 2023, at 10:21 AM, Mike Katz via cctalk <cctalk@classiccmp.org> >> wrote: >> >> the drive would see half the new data and half the old data. > > I think that explaining it this way can easily lead to an incorrect inference > on the part of an arbitrary hypothetical neophyte that what is going on in > the drive in such a case is that the head can equally well read either the > old data or the new data but the controller can’t distinguish which is which, > or might return old data, or might return new data, or might indiscriminately > return some old data and some new. > > What the drive reads in such a case is noise, because the wider head picks up > a superposition of the old (wide) 48tpi track data AND the new (narrow) 96tpi > track data, simultaneously.
Double-stepped disks written at 96 tpi are perfectly readable on a 48 tpi drive if the disks are bulk-erased first. I've done this using a videotape eraser and later, a DC eraser made up of two ring magnets from an old magnetron, spaced perhaps 3-4 mm apart with like poles facing each other. Just pass the disk around the gap. Works a treat. --Chuck
