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Devices that use light to store and read data have been the backbone of data storage for nearly two decades. Compact discs revolutionized data storage in the early 1980s, allowing multi-megabytes of data to be stored on a disc that has a diameter of a mere 12 centimeters and a thickness of about 1.2 millimeters. In 1997, an improved version of the CD, called a digital versatile disc (DVD), was released, which enabled the storage of full-length movies on a single disc.
CDs and DVDs are the primary data storage methods for music, software, personal computing and video. A CD can hold 783 megabytes of data. A double-sided, double-layer DVD can hold 15.9 GB of data, which is about eight hours of movies. These conventional storage mediums meet today's storage needs, but storage technologies have to evolve to keep pace with increasing consumer demand. CDs, DVDs and magnetic storage all store bits of information on the surface of a recording medium. In order to increase storage capabilities, scientists are now working on a new optical storage method called holographic memory that will go beneath the surface and use the volume of the recording medium for storage, instead of only the surface area. Three-dimensional data storage will be able to store more information in a smaller space and offer faster data transfer times.
Holographic memory is developing technology that has promised to revolutionalise the storage systems. It can store data upto 1 Tb in a sugar cube sized crystal. Data from more than 1000 CDs can fit into a holographic memory System. Most of the computer hard drives available today can hold only 10 to 40 GB of data, a small fraction of what holographic memory system can hold. Conventional memories use only the surface to store the data. But holographic data storage systems use the volume to store data. It has more advantages than conventional storage systems. It is based on the principle of holography.
Scientist Pieter J. van Heerden first proposed the idea of holographic (three-dimensional) storage in the early 1960s. A decade later, scientists at RCA Laboratories demonstrated the technology by recording 500 holograms in an iron-doped lithium-niobate crystal and 550 holograms of high-resolution images in a light-sensitive polymer material. The lack of cheap parts and the advancement of magnetic and semiconductor memories placed the development of holographic data storage on hold.
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10-05-2012, 01:20 PM
PRESENTATION.pptx (Size: 359.3 KB / Downloads: 28)
#Data from more than 1,000 CDs could fit on a holographic memory system.
# Most computer hard drives only hold 10 to 40 GB of data, a small fraction of what a holographic memory system might hold.
# Holographic memory offers the possibility of storing 1 terabyte (TB) of data in a sugar-cube-sized crystal.
# A terabyte of data equals 1,000 gigabytes, 1 million megabyte or 1 trillion bytes.
To produce a recording of the phase of the light wave at each point in an image , holography uses a reference beam which is combined with the light from the scene or object (the object beam). Optical interference between the reference beam and the object beam , due to the superposition of the light waves , produces a series of intensity fringes that can be recorded on standard photographic film . These fringes form a type of diffraction grating on the film , which is called the hologram .
CODING & SIGNAL PROCESSING
In a data storage system (holographic memory) ,the coding & signal processing is to reduce the BER (binary encoded representation) .This is stress free and less possibility of error is there .It is easily understandable to the user .Coding and signal processing includes several qualitatively distinct elements which are described as below :-
ECC (Encoder) :- It ends the repetition of the data and provide protection from various noise sources .Then it passes to modulation encoder which then fits the data to the channel which then saves the data to be corrupted by channel errors and give a clear channel output .
INTERPIXEL INTERFERENCE :- In this the amount of energy at one particular pixel infects data at near by pixel .This arises from optical diffraction in the imaging system .