<title>Archival Optical Disk Data Storage</title>

Abstract

The optical disk has become a viable candidate for mass digital data storage. Its unique characteristics make it suitable for archival, wideband, high density record and playback applications as well as those requiring fast access to a large data base. RCA has been pursuing the development of such systems for government mass data storage and retrieval requirements. This work is centered around a unique "tri-layer" optical disk structure, which offers high sensitivity and signal-to-noise ratio (SNR) at very high packing densities. The two major areas of pursuit are record and playback at data rates of 200 Mb/s or more and multiple-disk record and playback units for very large on-line capacities. Record and playback at high data rates is achieved through simultaneous multiple, parallel-channel operation. Present day solutions involve splitting the output from a single high-power argon laser into multiple beams, modulating each beam independently, and focusing them onto a rotating optical disk to simultaneously form a closely spaced series of data tracks. Single-channel rates of 50 Mb/s and multiple-channel rates of 150 Mb/s have been demonstrated on laboratory breadboard equipment. Designs for equipments that will operate at 400 Mb/s are being pursued for implementation in an engineering development model. Concept designs for multiple disk record and playback systems are centered around two "jukebox" configurations, which can provide fast automatic access to large on-line data stores. A feasibility design for a reader unit with an access time of three seconds to 1013 bits (100 disks) has been performed. A second concept provides a capability of both record andplayback of 50 Mb/s with an access time of seven seconds to 1013 bits. This unit features an expansion capability for servicing multiple simultaneous user requests. Both "jukebox" configurations have been developed for large archival mass memory systems. These systems require a storage capability of 1013 bits (1014 bits on-line) at record and playback data rates of 50 Mb/s and access times of 3 to 15 seconds.