Erasable digital video disk with reference clock track

Abstract

An optical disk and compatible optical disk drive enabling erasable (rewritable) optical disks to have the same format and capacity as read-only or (recordable) write-once optical disks. A reference clock track and optional additional prerecorded phase synchronization patterns are provided to enable writing of any random sector with frequency and phase matching of a random sector to the preceding and following sectors. The reference clock track and other phase synchronization patterns eliminate the need for preambles and extra space for speed variation. In a first embodiment, a disk has multiple layers, with at least one rewritable data layer and at least one reference layer. A spiral track on a surface of the reference layer has prerecorded patterns to be used for clocking. In a variation of first embodiment, the reference layer is also used for radial tracking control, eliminating the need for predefined tracks in the rewritable data layers. The reference layer is produced using the same technology as for read-only media, and is therefore very precise, low cost, and permanent. An additional laser system may be required to read the reference layer. The rewritable data layers may be unpatterned prior to writing. Alternatively, the rewritable data layers may include embossed sector or block headers to augment clock phase precision. In a second example embodiment, a single circular permanent (non-erasable) clock track is provided on a rewritable medium. The disk is then divided into radial zones, so that within each zone, the angular velocity of the disk is constant. A clock signal from the permanent clock track is then ratioed for each radial zone.