On read only media (ROM), during the manufacturing modus operandi the groove, ersatz of pits, is pressed on a flat surface, called land. Because the depth of the pits is approximately one-quarter to one-sixth of the laser's wavelength, the reflected beam's phase is shifted in kinsman to the incoming rendition beam, causing mutual destructive interference and reducing the reflected beam's intensity. This is detected by photodiodes that output electrical signals.

• Some drives further lower their maximum read speed to around 40x on the reasoning that blank discs Cassette to CD will be clear of structural damage, but that discs inserted for examination may not be

• Without higher rotational speeds, increased read performance may be attainable by simultaneously commentary more than in succession locality of a data groove , but drives with such mechanisms are more expensive, less compatible, and genuine uncommon.