Wait a sec--a "fixed disk" is just that--that medium is *not* removable. So, something like a Shugart SA-4000 is a fixed 14" disk drive. A drive using disk packs is a "removeable media" drive. Two birds of very different colors. Have a look at http://www.bitsavers.org/pdf/cdc/discs/40823100D_853_Maint_Feb69.pdf for a manual on CDC's answer to the IBM 2311. There's a good description of the threaded-spindle pack mounting there, as well as the head-load mechanism. For a fixed 14" drive, have a look at: http://www.bitsavers.org/pdf/shugart/39005-1_SA4000_OEM_Apr79.pdf Both use fractional-horsepower induction motors; the CDC drive uses a 3-phase motor that's probably somewhere around 1/3 hp (the specs don't say, but the start/run current ratings give a clue). The Shugart fixed drive uses a single-phase motor that's around 1/8 hp. Assuming that the motor can overcome the frictional losses and interia of the media assembly, the actual motor rating probably isn't terribly critical. Both use belt-drive. Cheers, Chuck