What rotational schemes do HD DVD discs employ?
HD DVD-ROM/R/RW are currently read and written using Constant Linear Velocity (CLV) while HD DVD-RAM employs Zoned Constant Linear Velocity (ZCLV). As is the case for CD and DVD, Constant Linear Velocity (CLV) maintains an even data transfer rate as the optical head of the recorder, drive or player reads or writes from the inner (ID) to outer (OD) diameter of the disc. At 1x, the rotational speed of an HD DVD-ROM/R/RW disc decreases from roughly 2620 RPM to 1089 RPM (ID to OD) to maintain a constant linear velocity of 6.61 m/s. HD DVD-RAM employs a Zoned Constant Linear Velocity (ZCLV) scheme. The disc is divided into 19 zones with rotational speed kept constant within each but varied from zone to zone resulting in a relatively even data transfer rate and linear velocity of 5.64 to 6.03 m/s.
