Pregroove

Pregroove is a term used in disc media to describe a groove or guide structure that exists before the main data area. It serves as a reference for equipment to position itself accurately and may carry information used by the device to calibrate its optics or mechanics. The pregroove itself is not typically used to store user data.

On optical discs such as CDs, DVDs, and Blu-ray discs, the pregroove is a precisely defined groove in the disc substrate that the drive’s tracking and focus systems can read. In writable formats like CD-R, DVD-R, and Blu-ray Disc Recordable, the pregroove often includes a wobble pattern that encodes timing, addressing information, or disc format details. The drive uses this wobble to generate a clock for data writing and to determine the disc’s start position, capacity, and type. User data are written to the data track, while the pregroove provides the guiding reference and timing information.

In standard read-only discs, the pregroove can also serve as a reference for the lead-in and lead-out areas, helping the drive establish correct starting points for reading sessions.

In the context of vinyl records, the term pregroove is not part of the standard terminology. Vinyl playback centers on the playable groove, with related concepts more typically described in terms of lead-in, run-out, and dead wax rather than a separate pregroove.

See also: wobble groove, lead-in, lead-out, dead wax.