26 Mar
2000
26 Mar
'00
11:10 a.m.
On Mar 26, 16:16, Richard Erlacher wrote:
I'm not sure I am the one who should wake up here.
I would repeat "It
doesn't matter whether the diskette is a 1.2 MB one or a 360K type" but
it
does depend what sort of drive it is.
No, Fred is right. There are plenty of drives designed to use single
density or double density disks at 96 tpi, and disks cerified for such use,
and they work perfectly reliably for 80 tracks, SD or DD. Historically,
such drives predate 1.2M (HD) drives. Provided you use SD/DD media in a
drive using the correct write current, and providing there isn't any other
leftover rubbish for the wider heads in a 48 tpi drive, any reasonably
well-aligned 48 tpi will handle those disks just fine. However, no 48 tpi
drive I have ever heard of is designed to use HD 1.2M media, and if you try
it, it will give trouble sooner or later. All the evidence indicates that
the major factor is the magnetic coercivity of the media.
[...] the fact that the heads designed for 48tpi will
write a
significantly wider swath on
the diskette than the 96tpi drive can erase. Consequently, and I'll bet
you've had this experience, you can format a bulk erased diskette to
48tpi
with a 96 TPI drive and have it work for a while.
The more the diskette is written, by the 48tpi drive, the harder it
becomes
for the 96tpi drive to erase its writing,
Again, no. Providing you're only reading back the part overwritten by the
96 tpi drive, this is not true. It only matters if you both write with 48
tpi, overwrite with 96 tpi, and then try to read back with a 48 tpi drive
-- which is not what was being discussed. And it doesn't make any
difference whether the 48 tpi drive writes once or one thousand times, the
magnetic field strength is the same!
and, of course, the 48TPI drive
will have the most trouble because the signal not erased in the 96tpi
drive
is perceived by the 48tpi drive as noise, while the
signal written by the
96tpi is written at a lower level to begin with, since the drive relies
on
the higher coercivity of the medium to generate a
larger signal amplitude
if
that factor is to come into play at all.
No, it doesn't rely on the higher coercivity, not when it's writing single
or double density. It only does that for High Density.
--
Pete Peter Turnbull
Dept. of Computer Science
University of York