NFG
Joined: 18 Dec 2006
Location: Brisbane.au
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 Posted: Wed Feb 14, 2007 2:46 am |
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| Thats assuming that data is recorded to the disk at a uniform bits per unit distance as opposed to a uniform bits per revolution. This assumption also assumes that the sampling rate from the center out is not uniform but rises (steadily?) as it goes outward. So the laser would need to determine its distance to the center and adjust its sampling rate continuously as it read data. So basically im calling BS. |
This is why LDs had two kinds of discs: CAV and CLV. Constant angular velocity and constant linear velocity. In the former there was a fixed number of bits in every rotation. In the latter the disc would actually slow down to read them... But this is different, as with video you need a fixed bit-rate to feed the electron guns, LDs didn't use digital video and couldn't buffer the signal.
In any case, it's true: there are more bits per rotation at the outside edge of a CD than the inside. If they were more widely spaced out you'd probably see the gaps between them, like you can on a CAV LD. And, it's gotta be said, that would be stupidly wasteful.
And, duh, the laser KNOWS how far out it is from the center, it's not a record player. What happens when it seeks to a new file? It whips out to a point a specific distance from the center.
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