🚀 go-pugleaf

In article <273@csustan.UUCP> smdev@csustan.UUCP (Scott Hazen Mueller) writes:
>It's been done before.  I don't think that it is quite done by changing the
>clocking rate, but I do know of disk drives that vary the number of sectors
>per track in order to fit the most data on the disk.  I believe that the
>lowly Commodore 64's disk drive is one such device.
>

Indeed, the Commodore 1540/1541/1571 5.25 in. floppy drives do indeed vary
the number of sectors/track.  There are three zones with from 17 to 21 sectors
per track in each of the zones.  Additionally, the drive controller changes
the clocking rate as well.  There are 4 clocking rates available to the DOS
for use in the process.  Some of the ``copy protect'' schemes on the CBM drives
use variations in the clock rate to make copying difficult.
	One additional not about the CBM drives though, they use a 5-for-4
GCR encoding scheme to record the data, this supposedly allows them to get
away with higher densities on cheaper media.
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Gregory G. Woodbury				The usual disclaimers apply
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