Re: On a side note
"The read/write heads were not always calibrated identically on different machines."
That was a common problem - the fact that you can _buy_ audio calibration cassettes escaped most people's notice. The fact they're about $100 apiece and you need at least two - 1kHz and 10kHz - is offputting for many more. (you need to calibrate both cassette spindle/drive motor speed AND head alignment - with the speed being surprisingly out of whack on a lot of mechanisms)
For floppy drives it was a bit trickier but calibration disks did (and do) exist if you're willing to stump up for them AND can read an oscilloscope. The demise of stepper motors driving linear positioning strips and uncontrolled spindle motors(*) made absolute track calibration less of an issue anyway
(*) These had a rudimentary trimpot speed control in the end of the motor just like cassette mechanism but no feedback mechanism telling the drive what speed the disk was rotating at. That coupled with "rubber band drive" between the spindle motor and spindle (the motors didn't have enough torque for direct drive) meant "wow and flutter" caused by varying friction between the floppy disk and its case was a serious issue. The original head stepper motors had no positional feedback to locate the first track and would just seek N times until they "should be" at the end of travel. Newer drives use a worm gear to slide the head, have an optical sensor for the end of travel (not just the hole in the floppy) and can hunt more precisely to locate the index track in the case of misaligned tracks.
Biting the hand that feeds IT
