Applications For A High Capacity, High Data Rate Optical Disk Buffer

Abstract

ABSTRACT A high performance Optical Disk Buffer concept for Terabit storage and Gigabit/s data rate is being developed along modular lines, such that additional new configurations for specific applications are evolving. This paper describes progress in the development of the basic modular subsystems, and correlates the modular performance with an extended family of Optical Disk Buffer configurations and system applications. 1. THE OPTICAL DISK BUFFER CONCEPT The demand for high performance digital data processing in the U.S. Government has spurred the development of optical disk recorders. The availability of re-writeable recording media-^'2 has made possible a family of high data rate, high capacity, data storage buffers based upon optical disk technology. Figure 1 shows a multi-disk concept originally formulated under a U.S. Government contract to simultaneously address four demanding requirements: High Capacity, High Data Rate, Large Data Blocks, and Random Access3 .The need for high capacity was expressed as a goal of one Terabit of data storage. The concept design met this need by placing twelve double-sided disks on a common shaft, with each disk surface to provide 40 Gigabits of storage. The large capacity per surface derives from the close track spacing and submicron recorded spot size that the optical system can provide, and from the use of disk media 356 mm (14 inches) in diameter.The need for high data rate established a goal of 133 Mbits/s for each active surface. Here, the development of the laser diode array4 permits multiple tracks to be recorded simultaneously through a common optical system, with each track accurately spaced, and each laser diode operating at a conservative data rate for a high reliability design application.A growing need for a buffer which could record very large data blocks was addressed by the use of a spiral track format. With the spiral format, multi-megabyte data blocks, and streaming data requirements as well, could be met without the track-to-track relocations that a concentric-ring track pattern would necessitate.Random access to record or retrieve data is provided by independent operation of each Electro-optic (EO) Head and disk surface set. The modularity of each EO Head and its matching disk surface is also the key to building Optical Disk Buffers configured to specific operational and functional requirements.