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From: ggw@ethos.UUCP (Gregory Woodbury)
Newsgroups: comp.arch,comp.periphs
Subject: Re: an idea for higher capacity disks
Message-ID: <899@ethos.UUCP>
Date: Tue, 11-Nov-86 20:54:04 EST
Article-I.D.: ethos.899
Posted: Tue Nov 11 20:54:04 1986
Date-Received: Wed, 12-Nov-86 21:50:18 EST
References: <1256@hoptoad.uucp> <273@csustan.UUCP>
Reply-To: ggw@ethos.UUCP (Gregory Woodbury)
Followup-To: net.arch,net.periphs
Distribution: world
Organization: Humanities Forum at ethos, Durham, NC
Lines: 21
Summary: Commodore floppies do it
Xref: mnetor comp.arch:13 comp.periphs:5

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.
-- 
------------------------------------------
Gregory G. Woodbury				The usual disclaimers apply
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