BY CHINMAYEE BAITHARU
WHAT’S THE NEW BUZZ
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.
Holographic data storage systems use the volume to store data. It is based on the principle of holography
WHAT IS HOLOGRAPHY?
Holography was invented in 1947 by the Hungarian-British physicist Dennis Gabor (1900-1979), who won a 1971 Nobel Prize for his invention.
Holography is a technique of recording patterns of light to produce three dimensional object.
COMPONENTS OF HOLOGRAPHIC MEMORY
The holographic memory system is made up of the following basic components:
Blue-green argon laser
Beam splitters to spilt the laser beam
Mirrors to direct the laser beams
LCD panel (spatial light modulator)
Lenses to focus the laser beams
Lithium-niobate crystal or photopolymer
Charge coupled device camera
RECORDING OF DATA IN HDSS
DETAILS ABOUT CCD
CCD is a 2-D array of thousands or millions of tiny solar cells, each of which transforms the light from one small portion of the image into electrons. Next step is to read the value (accumulated charge) of each cell in the image. In a CCD device, the charge is actually transported across the chip and read at one corner of the array. An analog-to-digital converter turns each pixel's value into a digital value. CCDs use a special manufacturing process to create the ability to transport charge across the chip without distortion.
WHAT IS SLM?
A spatial light modulator is used for creating binary information out of laser light. The SLM is a 2D plane, consisting of pixels which can be turned on and off to create binary 1.s and 0.s.
PAGE LEVEL PARITY BITS
Once error-free data is recorded into a hologram, methods which read data back out of it need to be error free as well. Because page data is in the form of a two dimensional array, error correction needs to take into account the extra dimension of bits. When a page of data is written to the holographic media, the page is separated into smaller two dimensional arrays. These sub sections are appended with an additional row and column of bits.
Unlike magnetic storage mechanisms which store data on their surface, holographic memories store information throughout their whole volume.
Fortunately, the properties of holograms provide a unique solution to this dilemma.
This method of storing multiple pages of data in the hologram is called multiplexing.
One possible application is data mining. Data mining is the process of finding patterns in large amounts of data.
Another possible application of holographic memory is in petaflop computing. A petaflop is a thousand trillion floating point operations per second.
Holographic memory can be used as extended DRAM with 10ns access time,
Holographic memory vs. conventional storage devices
In contrast to the currently available storage strategies, holographic mass memory simultaneously offers high data capacity and short data access time
(Storage capacity of about1TB/cc and data transfer rate of 1 billion bits/second)
Holographic data storage has the unique ability to locate similar features stored within a crystal instantly.
Because the interference patterns are spread uniformly throughout the material, it endows holographic storage with another useful capability: high reliability.
No rotation of medium is required as in the case of other storage devices.
It can reduce threat of piracy since holograms can’t be easily replicated.
Manufacturing cost HDSS is very high.
And there is a lack of availability of resources which are needed to produce HDSS.
Writes in the same fashion can degrade previous writes in the same region of the medium.
The re-illuminated reference beam used to retrieve the recorded information, also excites the donor electrons and disturbs the equilibrium of the space charge field in a manner that produces a gradual erasure of the recording.
In the past, this has limited the number of reads that can be made before the signal-to -noise ratio becomes too low.
The future of holographic memory is very promising. The page access of data that holographic memory creates will provide a window into next generation computing by adding another dimension to stored data.
Holographic memory will most likely be used in next generation super computers where cost is not as much of an issue.