Re: Floppy disk density

[Andy McFadden <fadden@fadden.com>]

Michael J. Mahon <mjmahon@aol.com> wrote:
> The inner track has a radius of about 1.375" and the outer track has
> a radius of about 2.4".  If the motor speed and the recording bit rate
> are constant, as they are for most floppy drives, then the capacity of
> the shortest track determines the capacity of all tracks  For a 5.25"
> diskette, if the motor speed or bit rate were varied to keep bit density
> approximately constant, the capacity of the diskette would increase
> by a factor of: 0.5 * ([max radius]/[min radius] + 1), which in this case
> works out to about a 37% increase in capacity.

The difference between PC and Apple 3.5" disks is much closer (720K vs
800K, one is 90% of the other).  This may be because the difference in
circumference for the outside and inside track of a 3.5" disk is less
significant than for 5.25".

In any event, you'd probably want to break the disk into ZCAV zones
for practical reasons: any increase in bits per track that results in less
than a full sector gain doesn't help you.

I believe the 5.25" floppy drives for the Apple Lisa used some of these
tricks media to get as much as possible onto the disks (1MB?).  Of course,
the drives had dedicated CPUs...

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