An optical fixed data store

An optical fixed data storage system is described which is designed to hold 4 M bits of information on each exchangeable photographic plate. The store, intended as an integral part of a computing system, enables any of 65,536 69-bit words to be retrieved with a random access time of a few microseconds. Writing time for each data plate is approximately 1 hour. To record and retrieve the data, a spot is positioned on the face of a high resolution electrostatic cathode ray tube, and multi-imaged on to a photographic plate by means of a lens/square cross-section mirror tunnel/lens system. Word readout is achieved using one 11-stage photomultiplier as detector for each bit of the word.