System for preventing the overwriting of previously optically recorded data and for reading optically recorded data during writing

摘要

@ An optical file system in which a command to store data results in a write operation in the next available storage position. A single optical path is used for both reading and writing. By dividing the detector (10) in two equal parts (10A, 10B) along the direction of relative movement, it is possible to determine whether data has been written at a position which is in advance of the center of the area viewed by the detector. The write operation is conditioned on the output of the first part of the detector. Since the first part of the detector gives advance warning on the status of the oncoming data position, it is possible to switch from reading to writing without the requirement for a wasted revolution or wasted space. By dividing the signal resulting from a change of reflectance sensed during a write operation by a measure of the intensity of the write laser a read signal free of the write modulation is obtained.