17 Jun
2015
17 Jun
'15
11:06 a.m.
On Jun 17, 2015, at 1:50 PM, Johnny Billquist <bqt
at Update.UU.SE> wrote:
On 2015-06-17 19:40, tony duell wrote:
Interferometer would make sense, at least for drives of that era. I think modern drives
have track spacings small enough that a visible light interferometer may not be sufficient
any longer.
[Writing alignment disks]
Quite possible. But it also requires the movement control being different from a standard
drive, in order to drive at the precision, as well as the feedback from the inferometer.
As far as I know, in special machines mounted on
slabs on stone
weighting tons, standing on dampeners, so that you had absolutely
vibration free environment, and then a very precisely controlled head
control system that could write the tracks at the exact place they
I have an idea that some of these units used an optical interferometer to
determine the head position ...
True, but an RK05 doesn?t have servo data on the platter; positioning is done by reference
to an optical widget in the drive. So it depends on mechanical reproducibility being
significantly better than the track spacing. Higher density drives use on-pack servo to
avoid that constraint. And embedded servo avoids an additional constraint: accurate
positioning of one head relative to another.
paul
Incidentally, I once saw a procedure (maybe HP)
for rewriting the servo surface of
a fixed/removeable drive in the field. It used special electronics, but not any special
mechanics. It went like this :
[...]
Well, a drive like the RK05 can also be reformatted in the field. So it all depends on
the drive?