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

Jim Kinney jim.kinney at gmail.com
Wed Mar 4 09:35:26 EST 2009


I'm pretty sure the rotational speed for any given value is not fixed
but variable based on head location. If speed is fixed, bit rate
increases with increased distance from spindle. I would expect the
data rate to have a factor of pi in it somewhere since it relates to
radius and circumference.

On Wed, Mar 4, 2009 at 8:13 AM, Devnull <devnull at iamdevnull.info> wrote:
> Hi, this is kind of off-topic, but I thought that you might be able to
> shed some light on this. I have done a science project that determined
> the correlation between the rotation speed of a CD and the data speed
> of the CD. I used the eject command to change the speed of the CD
> drive, and the dd command to read all of the data off the CD. I even
> used an Ubuntu CD for the tests :) I would set the CD drive to every
> speed between 1 and 45, and record the time, bps, etc. Now my question
> is this: When I plotted the graph, the graph indicated that there was
> an exponential correlation between the data, but from what I know,
> there should be a linear correlation. What I thought was that 2x is
> twice the speed of 1x, 3x is thrice the speed of 1x, etc. This would
> suggest speeds proportional to x, but I am not getting these results.
> Please correct me if I am wrong. Thanks.
>
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James P. Kinney III


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