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


Reply via email to