Is a CD read faster near the center or near the edges?

[SubZeroX]

In CLV (constant linear velocity) is a CD read faster near the center or near the edges? I thought it's faster near the edges, but according to my physics instructor, it's faster near the center.

When I run tests like Nero to test my CD drives the reading speed always increases as time goes by, which makes me think that the speed increases as the beam is focused further and further away from the center of the disc.

What the guy said was that since there is less data in the small circumference near the center of the disc, the spinning speed must increase to ensure a constant flow of data. Whereas in the outer edges, more data is stored so it doesn't have to spin as fast to get a constant flow of data.

Kinda confused...

 

[LiekOMG]

Faster at the edge, slower near the center

 

[Alphazero]

In CLV read speed is kept around the same throughout the disc, but it does get a little faster toward the outside edge.

In CAV (Constant Angular Velocity) drives, reading is much faster on the outside.

 

[SubZeroX]

hmm, maybe my CD drives use CAV and not CLV, that's why they read faster near the edges.

Thanks guys.

 

[TDSLB]

It's at the edges, a circliar disc has to spin faster on the outsides because the farther from the center point of a circle you get. The farther around you have to go.

Think of a race track, when they the race the people on the outside are farther up along the track because they have to go around a wider turn and therefore more distance. Thats how I always remembered it.

I could be wrong but I really didn't think that difference in reading speeds was even worth mentioning, least, untill you started reading DVD's.

 

[MWink]

hmm, maybe my CD drives use CAV and not CLV, that's why they read faster near the edges.

Yup. To my knowledge the fastest CLV drive was about 12x or 16x (except for the Kenwood drives).

 

[glen]

think of spokes on a bike wheel
I think data is written like that, so it has the same read speed no matter where it is

 

[Peetoeng]

Originally posted by: SubZeroX
In CLV (constant linear velocity) is a CD read faster near the center or near the edges? I thought it's faster near the edges, but according to my physics instructor, it's faster near the center.

When I run tests like Nero to test my CD drives the reading speed always increases as time goes by, which makes me think that the speed increases as the beam is focused further and further away from the center of the disc.

What the guy said was that since there is less data in the small circumference near the center of the disc, the spinning speed must increase to ensure a constant flow of data. Whereas in the outer edges, more data is stored so it doesn't have to spin as fast to get a constant flow of data.

Kinda confused...

Say you have two wheels: A with a radius of 1 and B with 2 (Don't worry about unit, we're just making comparison). And say that you want the wheels to run at a constant linear velocity of V.

Since w (angular velocity) = V/r

w(A) = V/1 = 1.0 V
w(B) = V/2 = 0.5 V

w(A) > w(B)

So, the cd will move with faster angular speed when reading data in the inner circle (A).

In case of CAV, the cd will rotate with the same (angular) speed. So, on inner circles, it will read less data because there's less data there. Think of the amount of data available in each circle as the length of its circumference.