Free: Stack of Victor or Sirius floppy disks
ard at p850ug1.demon.co.uk
Fri Mar 4 13:22:12 CST 2011
> On Thu, Mar 3, 2011 at 9:38 PM, Chuck Guzis <cclist at sydex.com> wrote:
> > On 2 Mar 2011 at 18:45, les at frii.com wrote:
> >> The Victor 9000 had a variable spindle speed...
> > One of the PC mags covered the disk operation back when. =A0The drive
> > spins more slowly when the head is on the outside tracks (i.e. CLV,
> > but ISTR that it isn't "constant", but rather zoned).
> CBM disks did that (one of the 65xx processors could affect the
> low-order two bits of a divide-by-N chip), and so did 400K Mac floppy
Actually, Commodore drives (at least the 8050 and 1541) kept the spidnle
speed constant and speeded up the data clock on the outside tracks. Same
idea, as I said in another message the are pros and cons to both methods.
> drives (you could hear the motor speed changing).
Yes. The 400K drive (which I believe is much the same as the drive Terry
was trying to fix) has an input for a PWM motor speec control signal. On
the mac, a counter is loaded from 8 bits of an unused video RAM location
at the end of each scan line (the other 8 bits go to a similar PWM
cirucit for the sound IIRC).
The Apple 800K drive is alos variable-speed, but IIRC the speed control
is handled entirely with the drive. The speed is set depending on what
cylinder the heads are on.
More information about the cctech