[ale] OT: CD drive and revolution speed correlation?

[Greg Freemyer]

On Wed, Mar 4, 2009 at 11:53 AM, Devnull <devnull at iamdevnull.info> wrote:
> On Wed, Mar 4, 2009 at 10:57, Jeff Hubbs <jeffrey.hubbs at gmail.com> wrote:
>> *Audio CDs* practice Constant Tangential Velocity in playback.  For
>> data CDs, it's more arbitrary; my understanding was that a "52x"
>> CD-ROM drive is only 52x at or near the outer edge, where the drive's
>> maximum rotational speed corresponds to the highest data rate.  It's
>> reasonable to say that CDs of all sorts have a constant tangential
>> data density independent of radius.
>
> I am not all that familiar with Constant Tangential Velocity, from
> what you have described here, I am guessing that it is similar to
> Constant Linear Velocity. Since the CD under testing was a data CD,
> does that mean that Jim was correct, insofar as the CD drive spins at
> the same constant physical speed during the entire read process. If
> that is correct, then it would be dependent on some pi-based function,
> right?

You don't need to worry about pi, but if you've forgotten your basic
math skills:

If you are reading data at 400 ips from a track 2 1/2 inches from the
center, then the rotation speed is:

rpm = 400 ips * (60 sec/min) / (2 * 2.5 * pi)

If at 1 in radius, just replace 2.5 with 1.

Greg
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