6 Jan
2014
6 Jan
'14
9:40 p.m.
On Mon, 6 Jan 2014, dwight wrote:
I would guess floppies were done the same
way as hard drives. They'd write a track and then
sprinkle some liquid ( I suspect like used for
magnaflux ) on it. They use a microscope with a
calibrated position to locate the data.
A good HOBBYIST way to check it.
A manufacturer would use a CASLIBRATED head positioner with
greater accuracy and different head than that of a consumer drive.
The Dysan Digital Diagnostic Diskette wrote multiple sectors of varying
mis-position within a track. THAT requires changing the head offset from
spec position multiple times DURING the writing of a track.
BUT, a homemade dgital alignment diskette could be made by writing an
entire track 0.1mm off position, another entire track at 0.05mm offset,
etc. It would not be as good, but it could still work, by comparing which
TRACKS were readable by the suspect drive. For example, if it could read
the correct track, and the 0.01mm too far in track, the 0.01mm too far out
track, the 0.02mm too far out track, and the 0.03mm too far out track, and
no others, then we would know that it was currently 0.01mm too far out.
(Just being able to read the correct track is absolutely NOT an adequate
indicator that the alignment is correct.)
Ideally, there should be multiple copies of each offset track.
The test read should include trying to read the given track by stepping
OUT to it to try to read, AND stepping IN to try to read, to allow for
lash/hysterisis/slop in the positioning mechanism.
Alternatively, if the hub clamp is offset from the spindle, then you COULD
write multiple offsets within a track, such as sector 5 is in correct
position, sectors 1 through 4 could be varyning amounts of too far in, and
sectors 6 through 9 could be varying amounts of too far out.
Determining which sectors are which could be done with post writing
measurement (use a narrow head on a known good aligned drive to see which
sectors are which), OR by positioning index before clamping (as would be
the case with 3.5").
A quetion for Tony, Chuck, Allison, etc. :
We need to deal with 48tpi (5.25 and 8"),
96tpi (5.25")
135tpi (3.5"),
and a few bizarre ones, such as 100tpi, etc.
Looking at the 48tpi example:
48 tpi is approximately 1/2mm track to track spacing.
The actual width of the track is approximately 1/4 mm.
What offsets from spec would be needed to be able to reasonably check for
alignment?
--
Grumpy Ol' Fred cisin at xenosoft.com