FUTURE CONCIEVABLE PRODUCTS

In principle, laser beams can be moved with no mechanical components, allowing access times of the order of 10 µs, faster than any conventional disk drive will ever be able to randomly access data. As in other optical recording schemes, and in contrast to magnetic recording, the distances between the “head” and the media are very large, and media can be easily removable. In addition, holographic data storage has shown the capability of rapid parallel search through the stored data via associative retrieval.

On the other hand, holographic data storage currently suffers from the relatively high component and integration costs faced by any emerging technology. In contrast, magnetic hard drives, also known as direct access storage devices (DASD), are well established, with a broad knowledge base, infrastructure, and market acceptance

Four conceivable product scenarios are shown in Figure 13. The first two scenarios use read/write media, while the latter two are designed for WORM materials, which are much easier to develop but must support data retention times as long as tens of years. The first scenario [Figure 13(a)] takes advantage of rapid optical access to a stationary block of media, resulting in a random-access time of the order of 10 µs. The capacity is limited to about 25 GB by the size of the block of media that can be addressed by simple, inexpensive optics. Such a device could bridge the gap between conventional semiconductor memory and DASD, providing a nonvolatile holographic cache with an access time that is between DASD and dynamic random-access memory (DRAM).

Using the same optical components but replacing the stationary block of media with a rotating disk results in performance characteristics similar to those of a disk drive, albeit with terabytes (1012 bytes) of capacity per platter [Figure 13(b)]. In the CD-ROM type of embodiment [Figure 13(c)], holographic data storage takes advantage of the fact that single-exposure full-disk replication has been demonstrated. The player for the holographic ROM is conceptually very simple: a CMOS camera chip replaces the photodiode from a conventional ROM player, and the reconstructed data page is then imaged with suitable optics onto that camera.

Figure 13

Combining one of the DASD-type R/W heads and possibly a number of CD-ROM-type readers, a robotic picker, and sufficient tiles of media, a data warehouse with petabyte (1015 bytes) capacity in a standard 19-inch rack is conceivable .While the access time to any of the stored files is determined by the robotic picker and will be of the order of tens of seconds, the aggregate sustained data rate could be enormous. In this scenario, the relatively high component cost of a read/write holographic engine is amortized over a large volume of cheap media to obtain competitive cost per gigabyte.