Free: Stack of Victor or Sirius floppy disks

Yes, The idea was to keep an appoximately constant-size bit cell on the disk. On 'normal' drives, there are a constatn number of bit cells per track, so they are larger on the outside tracks (which are, of ocurse, longer). The Sirius/Victor 9000 spun the disk more slowly on the outer tracks so as to keep the cells about the same size (and thus fitted more bit cells on theouter tracks). The Commodor 8050,. etc, kept the spidnel speed constant but changed the data rate clock to the encode. There are advntages and disadvantages to both methods. Keeping the data rate consstate simplifies the data recovery circuitry (and either allows for a simpler filter in the read amplifier or doesn't try to use said filter over too widr a range of fata rates). On the otehr hand, changing the spindle speed, and making sure it's got to the right speed, slows down track-to-track seeks. IIRC, the motors are controlled by an 8048 microcontroller on the disk conteroller board. I think it takes a pair of 4-bit inputs from one of the VIAs to set the speeds. -tony