Read data is de-interleaved and then analyzed by C1 CIRC circuitry that can locate and correct one or two error bytes in a 32 byte frame. If three or more error bytes are present, all bytes in the frame are flagged bad. Data is de-interleaved again and then analyzed by C2 CIRC circuitry that can correct up to four flagged bytes, or can locate and correct one or two error bytes. An E22 error indicates that the C2 circuit corrected two bytes in one frame. Each servo must then reacquire lock when the read laser spot exits the defect region.
Errors result both from the actual defect region as well as from the servo reacquisition region.
Some drives quickly achieve servo lock while others require more time, because different drives can use dissimilar designs for radial, focus, and constant linear velocity servos. Another practical justification arises from the deterioration of discs. These discs will soon become unusable when packaging, shipping, storage, and handling result in scratches, fingerprints, particulates, and other contamination of the readout surface. New discs that have zero E22 and E32 errors will have a much longer life under such conditions. Standards require air bubbles to be less than 0.1 mm in diameter, black spots surrounded by increased birefringence to be less than 0.2 mm, and black spots without birefringence to be less than 0.3 mm in diameter.