When your computer reads a dvd, the spiral data-track has to pass over a laser beam at a constant speed. for this to occur, the angular velocity of the disk must:

570-1600 rpm.

Explanation:

DVD is better at storage and also it spins 3 times more then the spin of the disk. So the DVD has  the angular velocity or rotational speed of 570-1600 rpm (rotations per minute). The reason behind having this range is that the disk spins faster near the center in comparison with the outer part. That is why we have got the range and not exactly a specific number. That's how the read head passes the same lengths in all times and radii. So the constant linear velocity or a constant speed which you have mentioned in the question is due to spin of the DVD faster at the outer edge and slower near the center.

i think it's 35 meters