Free: Stack of Victor or Sirius floppy disks

[Tony Duell]

> 
> The Victor 9000 had a variable spindle speed, I cant remember if the

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