[ Return to Special Projects ] As computer companies build faster machines and software companies create larger programs, computer storage devices have had to increase in capacity and speed in order to keep up. The move to smaller computer sizes and laptop computers has also meant that storage devices have also had to decrease in size. Two companies have taken the lead in research and development of storage devices. They are Quinta, a subsidary of Seagate, and IBM Research. II. A Look at Current Technologies Items such as this eight inch disc, this five and a quarter inch disc, this three and a half inch disc, and even newer discs like Zip discs and Superdiscs have many things in common, even though they mah not look very similar. Each one is made up of at least one magnetic storage disc. One of the first large capacity, random access storage devices was the IBM RAMAC. It was the size of a refrigerator and contained fifty spinning platters or discs, each two feet in diameter. Its maximum capacity was only five megabytes, which is the storage capacity of about three of today's three and a half-inch discs. The way the RAMAC stored data is much in the way current hard disc drives store data. What is pictured on this overhead is a crude and basic representation of the inside of a hard disc drive. Most hard disc drives will have more than one disc platter inside of them. Most disc platters in hard disc drives will hold information on both sides. The platters spin very fast on the drive spindle and the read-write head moves back and forth to cover the entire area of the disc platters. The magnetic surfact on the platter material contains billions of "bit spots," which is where a bit of information can be stored. When the read-write head is in write mode, and the software tells the head where it needs to be on the platter, each bit spot is either positively or negatively charged, depending on whether the bit is to be a one or a zero. When the head is in read mode, it reads whether or not the bit spot is already positively or negatively magnetized and then sends the result to the software. The mode of the head, as well as its location on the platters, is controlled by the computer's operating system and hardware. The way that companies increase the capacity of their disc drives is by decreasing the size of the bit spot. This decrease increases the disc's "areal density," or the number of bits that can be squeezed into a square inch of disc space. Originally it was thought that the areal density of the discs would not be able to become any larger than 2 million bits per square inch. Today, however, disc drive designers are approaching a limit determined by physics, not engineering ingenuity, which is somewhere around 40 billion bits per square inch. This limit, called the superparamagnetic limit, is due to temperature chamges within the disc drive. Beyond the superparamagnetic limit, random jiggling of electron spins, due to the temperature changes, is likely to cause the direction of the bit's magnetization to undergo spontaneous reversals during the life of the disc drive. In other words, a bit that is currently negatively charged could spontaneously become positively charged. This would result in the corruption and ruining of the data that is on the disc. This being the case, computer hardware manufacturers heve begun to look for alternatives to current magnetic storage devices. III. First Alternative - OAW Technology One alternative, called Optically Assisted Winchester, or OAW, Technology, has been developed by a company called Quinta, a research company that is partly owned by Seagate Technology. The OAW Technology combines optical components into the traditional magnetic storage systems of today. This hybrid system is not subject to some of the limitations that some of the current fully magnetic drives face. This alternative is already in place in many hard disc drives used in many high-end personal computers today. IV. Second Alternative - Holographic Data Storage System Another alternative has been under development by IBM Research. In November 1995, IBM announced a university/industry/government consortium that had began to develop a Holographic Data Storage System, or HDSS. The 32 million dollar project was put together to design data storage systems with 12 times the capacity of today's storage systems with input and output rages that are 10 times faster than is currently possible. Currently the organization is focusing on applications that would benefit from high-speed random access to large databases. The HDSS uses lasers to store and retrieve pages of electronic patterns within a volume of special optical materials instead of only being able to store information on the surface. In traditional holography, each viewing angle gives a different view of the same object. In holographic storage, however, instead of presenting another view, a different page of information is presented. Up to 10,000 pages of information, each one holding one megabit of information, has been stored in a piece of special optical material the size of a sugar cube. This means that 1250 megabytes, or just over 830 three and one-half inch floppy discs, can be stored in material no larger than a sugar cube. The setup of the holographic image and the laser means that each page of information in the optical material can be accesses simultaneously. This results in extremely high-speed data input and output. Speeds of 125 gigabytes per second have already been reached. V. About Holography The heart of the HDSS system is holographic images or holograms. Traditional holograms are three-dimensional images recorded on a light-sensitive film or plate. Scientists had tried for many years to stop moving light waves and to record them in a still state. The idea was then to release the waves at a later time, when they would continue on their way to make images. This is the basis of holography. The idea of holography was first thought of by the Hungarian-born, British physicist Dennis Gabor in 1947. He was unable to actually make his idea work because there was no equipment available to him that coule be used to make a successful hologram. At the time, the only main light source was the sun or electric bulbs. The problem is that these lights give out only white light. Because white light is composed of many colors, the image was distorted. This distortion was caused by the fact that the holographic plates are designed to only stop light of one certain wavelength or color. The other colors and wavelengths of the white light caused interference in the plate. It wasn't until the invention of the laser twelve years later that this problem was corrected. Lasers produce a very pure and concentrated light of exactly one frequency, or one color. This ended the distortion of the image because the laser can produce the exact wavelength that the holographic plate is made for. When a hologram is made, laser light is aimed at a beam splitter, usually a prism. This beam is split into two separate beams of light. One is called the reference beam and the other is called the object beam. The reference beam is widened by a lens or a curved mirror and then is reflected directly at the holographic film or plate. The object beam reflects some of the light towards the holographic plate. This interference pattern is actually the combined wave patterns of the two beams, which have become stationary. In order to view the hologram, a laser beam is shined through the holographic plate. This reactivates the light wave pattern and projects the object in front of the plate in three dimensions with remarkable detail. VI. Conclusion Developing several key components for the system is the initial goal for the HDSS team. The first is to develop a high-capacity, high-bandwidth light modulator, which is used in the system for data input. The second is to develop optimized sensor arrays for data output. Finally, the third is to construct a high-powered, red-light, semiconductor laser. The program's ultimate goal is to combine all of the components into optimized systems that will demonstrate once-write and rewritable holographic data storage. For the personal computer industry, the Holographic Data Storage System is currently not practical nor is it likely to be seen in the near future. It is however, practical for applications that are made up of large databases, such as for government agencies. It is a technology that people should be looking for becoming more and more popular as development continues. |
