On 2015-06-17 19:40, tony duell wrote:
[Writing alignment disks]
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
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.
should be. I think the alingment packs even have some tracks
intentionally offset from true center in order to check signal strength
when heads are slightly off track as well.
They normally have eccentric tracks so that the signal amplitude varies as
the disk turns. Look at that on a 'scope and adjust for the right bits being
the same amplitude and you're on-track.
I didn't know that tracks would be recorded eccentric. That's interesting.
Same kind of equipment was used to actually do the formatting of disks,
as they cannot be formatted by the disk drives themselves.
While the servo surface can't be re-written in the field (that is what
determines
head positions, after all), I see no reason why the data surfaces can't be
reformatted on a drive which has a separate servo surface like the RK06/07
Oh, agree. As long as the servo track is ok, the rest is easy. I was
specifically referring to the servo tracks. (Which on something like the
RL drives is embedded with the data.)
On such drives 'head alignment' really means getting the data heads lined up
with
(or the right offset from) the servo head.
Yes.
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...
Johnny
