From: "David Griffith" Subject: 8-inch drive substitutes model use media? Stepping rate and head-load timings will vary between drives. Sometimes dramatically (e.g. Persci's!) Jumpering of drives for things such as drive ready, disk change, etc. can get hairy unless you have documentation for both the "original" and "target" drives. Jumpering details can vary between different board revisions. Often transliterating the jumpering needed is easy; other times you think you did it right but there are gotchas you don't see until you look at schematics or pull out your scope. In industrial uses sometimes you see door-lock and disk-eject solenoids - available on many models but not commonly found in many circumstances. (These are also options on some 5.25" and 3.5" drives...) Some drives are capable of remotely spinning up and down. As Nico mentions, some use 50Hz AC for the drive motor, some use 60Hz AC for the drive motor, and others run the drive motor from the +24VDC. And as Nico alludes to, some need just +5/+24V and others need some negative power supply for the electronics and others need line AC for the motor. Often the drive itself is behind some panel/bezel and the holes in the panel must match the holes in the drive :-). Some drives are distinctly non-standard in terms of dimensions, even if they come from "standard" manufacturers (there were some weird-ass Shugarts out there.) Tim.