The growth in demand for digital storage capacity exceeds 60% per year. Facilities such as storage area networks, data warehouse, supercomputers, and e-commerce related data mining require ever-greater capacity in order to handle the volume of data to be processed. In addition, with the advent of high bandwidth Internet and data intensive applications such as high definition television (HDTV), video and music on demand, even smaller devices such personal video, mobile phone etc., will in the next two to three years demand 50 to 100 gigabyte and terabyte capacities. No less important is the growth demand for faster data access and reading. For instance, high definition TV, video and music on demand applications require over terabit per second reading speed. Such higher speeds in conjunction with huge capacity can be implemented only by means of parallel access to any part of the information on the carrier. The current data/information are stored on magnetic disc drive HDD, tape and optically (compact disc CD and digital versatile disc DVD). Roughly 10% of the information will be stored on magnetic disc drive HDD, the remaining are stored on tape and optical disc. Disc drive manufacturers recently have successfully demonstrated 120 Gb/in~2, while optical recording demonstrate 27Gb/in~2 Future increases in density in optical media are possible by taking the advantage of shorter wavelength laser, high lens numerical aperture (NA) or employing near field techniques. Creating double-sided media has increased optical data storage capacities. The future of optical recording will be based on three dimensional, which increases the capacity of a given volume of media, with the objective of achieving a cubic storage element having the dimensions of the writing/reading laser wavelength.
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