RK06 alignment pack

[Johnny Billquist]

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