[Writing alignment disks] I have an idea that some of these units used an optical interferometer to determine the head position 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. 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 On such drives 'head alignment' really means getting the data heads lined up with (or the right offset from) the servo head. 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 : Mount a good removeable pack Use the servo surface of that to position the heads (all of them) Step a track at a time, maybe with deliberate offsets (can be done) and write to the servo surface in the fixed disk stack Now use the rewriten fixed servo surface to position the heads and reformat the fixed disk data surfaces. -tony Johnny

[Writing alignment disks] It was probably still a voice coil mechanism, but with very differnet drive electronics. 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. 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

On 06/17/2015 11:56 AM, Johnny Billquist wrote: These pack formatters used air bearings to give the most vibration-free rotation of the spindle. They were generally pretty open units, not like disk drives, and were run in clean rooms by people wearing low-dust overalls. Jon

What is the difference between an RK06 and 07 ? Is it capacity? Could this pack be used to align an RK07 ? I ask because we have an RK07 at the Update Computer Club. /P On Wed, Jun 17, 2015 at 08:53:22PM +0100, Jarratt RMA wrote:

On 2015-06-18 08:16, Pontus Pihlgren wrote: Yes. The RK07 is double the capacity. I don't think so. The RK06 and RK07 used the same design for the packs, but the RK07 packs twice the capacity. I believe it is just doubling the number of tracks. But of course, that means that RK06 packs do not match what RK07 drive expects from track width and number of tracks. I didn't know. When did we get one, and from where? We had one many years ago that I dumped. We might still have the packs from that one around. Johnny -- Johnny Billquist || "I'm on a bus || on a psychedelic trip email: bqt at softjar.se || Reading murder books pdp is alive! || tryin' to stay hip" - B. Idol

Yes, in particular number of cylinders. Both have 3 heads and IIRC same number of sectors. The RK07 has narrower heads than the RK06. AFAIK the RK07 will not even read an RK06 pack (I am not sure the servo will manage to lock). AFAIK, no. If it could, I would have bought it (given I have a pair of RK07s) I also seem to remember that this pack is used with a special alignement meter, not a 'scope. And that there are special tools for moving the heads I found a sort-of user manual for this on bitsavers, but no schematics of the meter, so no easy way to replicate it. -tony