II. THE PROBLEM

1. Introduction

New Multimedia applications, and the normal day to day data operations are placing new demands on storage systems (Multimedia refers to the integration of text, audio, still images, video, and graphics into an easily manipulated digital format). These kind of documents require 10 to 1000 times the storage capacity required by conventional documents. Multimedia programs eat up a large amount of storage space. Each second of full motion, full screen video requires 30 frames of video information at the rate of almost a megabyte (MB) of computer data per frame. That is about 30 MB of information per second, or 1.8 gigabyte (GB) per minute. This amount is not generally available, particularly in portable systems, which is the most promising sector in this industry following the trend toward miniaturization and more compact computers.

Until now, multimedia storage has been achieved using the technique called "compression", which consists of the coding of data in fewer bits that normally done, to save storage space or transmission time. Specialized software automatically compresses and decompresses data. However the key to high-quality multimedia playback is the sustained throughput (uninterrupted transfer) of information. Without it, frames are lost during capture and playback. The result is poor production quality in the form of blips, lost frames and flicker (Barr, 1993).

For this and other reasons, multimedia producers and developers have learned to develop a healthy respect for computer storage technology. Storage is seen by many in the industry as the critical enabling technology for many new multimedia applications and to address its rapidly increasing requirements is the key to bring forward this new technology. Currently, this storage is provided by magnetic and optical technologies, and despite fantastic advances in these technologies, physical limitations are involved in getting data on and off of the conventional (mechanical) rotating devices. For example, disk based storage uses moving parts that poop out at a certain speed (Gibbs, 1993), and further progress in CD-ROM technology faces a fundamental limit: the pits that encode information on the surface of a compact disk can be no smaller than the wavelength of the laser light used to read them (Parish, 1990).

Evidently, the next giant leap in computer data storage capacity will have to come from elsewhere. In fact, the increased demand for significantly more storage capacity coupled with the development of the wide variety of applications have considerably taxed the ability of these storage systems. While this gap is temporarily hindering the emergence of multimedia, there is a rapidly growing pressure for such technology. The opinion of many industry leaders is that, whoever delivers a solution to the current storage capacity problem will dominate the information storage market of the future.

Efficient multimedia systems require high density, interchangeable media for the majority of their applications. These applications vary from the initial loading of software, to multimedia presentations, to simple back up of files located on the device. The general characteristics of storage devices for the multimedia product environment are:

a. Store information in a form that can be easily manipulated by electronics.
b. Safely store huge amounts of information, typically, one to more than a thousand gigabits so that it can be preserved indifinitively as archives.
c. Any part of the stored information can be read out or changed at any time with the shortest possible delay which, particularly for the fleeting intermediary data occurring in processing, is typically 1 msec or less.
d. Low power consumption ( 1 watt average )
e. Low cost per megabyte of memory (Less than one dollar per MB)

A new optical technology, called "Holographic Storage" may offer exciting possibilities, and the promise of being the most cost-effective solution to the storage requirements of multimedia computing than any existing or projected technology. The new technique enables the storage of digital information as three dimensional ( 3D ) optical holograms. Storing and retrieving data as two dimensional patterns of light, or pages, in a 3D volume of light sensitive crystal, provides the basis for holographic storage technology. Organizing data into pages instead of individual bits, and the use of lasers, provide access to speeds and orders of magnitude faster than the rotating devices of today (Mass storage devices have traditionally used magnetic and optical media which is under the control of a disk operating system). For example the fastest magnetic disk currently available takes over 5 hours to transfer what, theoretically, a holographic storage device could transfer in 1 second . This means that it can easily handle the demand of computing with images, or multimedia. This technology is based on photo refractive -uses light instead of electricity as in fiber optics- volume holographic storage (PVHS) techniques; it makes possible extremely fast, and potentially removable media. Holographic storage devices would be a good choice for systems that need to provide fast random access for the recording and playback of digital video and high throughput transaction-processing systems ( allows quick access to stored information ) at the lowest cost.

Today, holographic technology is like a plane ready to take off, gathering momentum for a jump that promises to take us to a new information environment. But all the favorable technical developments and the conceptual richness of holography itself, is never enough to have it achieve a status of mainstream technology. For holography to prosper and develop, some challenges and impediment to its progress, which can range from merely a lack of public understanding of the technology, to a limited science and technology base, to competition from existing technologies, must be overcome, and the following questions need to be considered in the current milieu of memory technologies:

- What feature combinations and performance does holography need to have to meet market demand and gain market acceptance?

- Is there a place under the sun for holographic memories? If yes, what specific role can be assigned to them in the memory markets of the present as well as of the future?



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