[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
