RK06 alignment pack

[tony duell]

[Writing alignment disks]

> > 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.

It was probably still a voice coil mechanism, but with very differnet drive
electronics.

> > 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.)

The RK06/07 do not have embedded servo. There are 2 disks, 4 surfaces in the pack. One is 
a dedicated servo surface. That cannot be rewritten in the field, AFAIK the data surfaces can be
reformatted.

> > 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...

Sure. The low-track-density drives like the RK05 (HP7900, IBM whatever) don't have a servo
signal on the disk. They have an optical position transducer on the positioner for head position
feedback. So they can get the heads into position on a totally blank disk. And thus can reformat
such a disk.

No the procedure I was thinking of was to re-write the dedicated servo surface on the fixed 
disk stack of a fixed/removeable drive that used a servo signal from the disk. I am pretty sure
it was an HP drive, maybe the 7905 or 7906 (I don't have either).

-tony