Editor: Advertised vs. actual speed differences with CD readers occur. One device claimed to read at 72x, when actual testing showed it read much slower than that speed. Similarly, many users are surprised when their 52x reader does not actually read at 52x over the entire surface of the disc. The same issue is occurring with CD and DVD writers.
CD and DVD writers are rated and compared using the “x” Factor which measures their speed in writing to a disc. This factor is based on one “x” being the speed at which an audio CD is played for CD devices, with a Similar but FASTER data transfer rate for DVD devices. Unfortunately for the buyer, this is not a particularly useful measurement, nor is it an indication of how fast the device actually is.
CD devices have three basic techniques of spinning the disc.
* CLV: This is the original technique for accessing CD discs and stands for Constant Linear Velocity. This varies the rotation of the disc so that the laser is moving over the disc surface at the same linear speed at the inside and the outside. Since the outside part of the disc is “longer” than the inner part, the disc is spun slower when accessing the outer part than at the inside part.
* CAV: In the past few years CAV (Constant Angular Velocity) devices have been introduced where the disc is spun at a constant speed. Most recent devices use this for reading and some variation for writing.
* Partial CAV (P-CAV) or Zoned CAV: These are variations where the rotation of the disc changes in relation to the position of the laser but less so than the original full CLV technique. The speed changes in a stepwise fashion rather than continuously over the surface of the disc.
