[KLUG Members] Revolutionary CD Drives & Rotations Per Minute (RPM)

[Bert]

magoo wrote:

>This factoid seems to be an error!  But it is not... 
>
>  
>
>>MORE FUN FACTS THAT WILL MAKE YOUR HEAD SPIN!!! 
>>A CD-ROM, for example spins from 539 rpm at the inner edge, to 210 rpm
>>at the outer edge. 
>>    
>>
>
>If the drive is spun at a constant velocity... both the inner edge 
>and the outer edge would be spinning at the same number of rotations 
>per minute.  A physicist could demonstrate this by showing that if 
>you draw a radii in black ink on the CD disc surface the entire line 
>will make the same number of revolutions per minute. 
>
>************************************************************** 
>   A CD drive does NOT use constant angular velocity (CAV)! 
>************************************************************** 
>
>< Bert wrote:>
>  
>
>>I don't know how you mean this but I don't think a cd can run on 2 
>>different speeds at the same time, however the speed in km/h (or 
>>miles/h) is on the outer edge much higer than on in the inner edge. 
>>Simple because the distance to travel, in the same time, is about pi 
>>(outer - inner) diameter bigger.
>>    
>>
>
>CD drives run at a variable speed depending on the track number!
>----------------------------------------------------------------------
>
I did not kow that! It reminds me of the old floppy drives used on an 
old apple macintosh. You could hear the thoose drives spin up and down 
depending on the track they read. I thought that all drives hard, floppy 
and also cd's did run on the same speed all the time.

>Constant Angular Velocity (CAV) and Constant Linear Velocity (CLV) 
>Magnetic and optical storage drives can rotate with constant angular
>velocity (CAV), or constant linear velocity (CLV). CAV, used by magnetic
>drives (and record players), is measured in RPM, and means that the read
>head sweeps the same angle, for the same amount of time, at all radii.
>CLV, used in CD-ROM, allows the head to read the same length of track at
>all times and radii, at a rate of 1.3 m/sec--also called 'reference
>speed, or scan rate.' CLV requires that the disc spin slower as the head
>moves to the outer edge of the disc; a CD-ROM, for example, spins from
>539 RPM at the inner edge, to 210 RPM at the outer edge. 
>
>http://hypertextbook.com/facts/2003/ClerbieMontilus.shtml
>
>http://www.cdpage.com/Compact_Disc_Glossary/glossarym.html
>
>< Bert wrote:>
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>>NB you should try putting a cd in a microway oven the effect 
>>is really  funny! (you may have to play with the watts put in
>>to get the best result)
>>    
>>
>
>This will permanently damage the microwave tube...  BAD IDEA! 
>
>
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