3.5" floppy drive question(s)

IIRC, the original Sony 3.5" drive was a 600RPM unit. Originally it was a single-sided unti, later there was a very similar double-sided one. These drives are not uncommon in classic computers -- HP used them a lot -- not just in logic analysers, but also in many of their floppy drive and hard/floppy drive units (HP9121, 9122, 9133V, 9133XV, 9133H, Integral PC, 9114A -- and that's just the ones I can see from here!). They are also used in at least some models of Apricot PC. There's a half-height ('slimline') Sony 600 RPM drive too, It shares many components with the Apple 800K drive (the main difference is in the control logic ASIC). It was used, for example, in the HP9114B. The HP9123 (dual foppy drive for the HP150-II) normally used the earlier DS drives, but I've seen one with slimline drives. The PCB has pads for both types of connector, there's a DIP switch to tell the firmware which drives are fitted. And yes I've repaired just about all of the above drives at some time or another... -tony