21 Jun
2001
21 Jun
'01
12:47 p.m.
What I read on the Web was that the first Shugart 801's could not
read/write DD, no matter what controller was attached to it. However,
later-manufactured 801's could handle both SD and DD.
Edwin
At 03:07 PM 6/21/2001 -0600, you wrote:
Tony's right about the Shugart 801's. Drives
don't determine the modulation
technique used to record the data. The "density" refers to the number of
bits
per linear inch on the track. Since that's really
not an adequate measure in
this context, its sensibly applied analog would be bits per revolution. The
head/media combination determines the number of flux changes per inch
(fcpi) and
single-density uses two flux changes per bit, while
double density uses
only one
(not exactly, but close enough). If the drive can
manage to swap the flux
direction quickly enough, which the '801 clearly can, then it's a
double-density
capable drive, which it is. Confusion arises from the
fact that, while
the '801
can read/write double density, its board-resident
"data separator" can't.
Also,
while the older '901 wasn't commonly used for
double density, it could manage
MFM if one used 250ns of write precomp. The '801 required only 160-180 ns.
Dick