icrofilm and microfiche are being bypassed for image storage because of their unsteady quality and long retrieval times. Users are choosing instead magnetic or optical devices, which pack a lot of images into a small space and offer swift data retrievals. The choice between magnetic and optical media depends mainly on speed and cost.
Although souped-up hard drives are being used for some smaller imaging projects, the preferred magnetic storage choices are tape cartridges and reels. Magnetic tape is significantly cheaper than optical media, storing images at less than a penny per megabyte. But it is not appropriate for long-term storage because of its susceptibility to data distortion caused by tape stretching and stray magnetic fields. And although there have been recent advances in large-capacity automated tape, optical media is still preferred for random-access searches.
High-speed tape devices commonly are used for medium-term storage (three to four years) while high-capacity, medium-speed tape devices are used for longer-term storage (up to seven years). Technological developments in the area of quarter-inch, 4mm and 8mm tape cartridges have resulted in reduced prices and increased data capacity. New automated tape subsystems from companies such as Exabyte and Storage Technology Corp. can store as much as 50 gigabytes (50 billion bytes) on one cartridge-compared to about 1 gigabyte for the average PC hard drive or optical system.
Yet optical disks have gained popularity because of their durability and random-access capabilities. The most common types of optical storage are CD-ROM (compact disk-read only memory), CD-Recordable and WORM (write once, read many) systems. All offer medium-capacity storage (about 300,000 printed pages) and high-speed access to data. The disks are available in a variety of diameters: 3 1/2 inch, 5 1/4 inch, 12 inch and 14 inch.
CD-ROMs cost relatively little to reproduce, so they are generally reserved for dictionaries, encyclopedias and other publications designed for mass distribution. WORM systems allow multiple-user access and store more images than CD-ROMS, but are also more expensive.
Optical systems are available in a variety of speed formats: 2x, 4x and 6x. New 6x drives from companies such as NEC and TEAC offer added zip for multimedia applications or high-volume text retrieval. And new high-definition CD-ROM units from Toshiba are ideal for full-motion video. CD-ROM jukeboxes, from Micro Design International and Plasmon Data, provide constant on-line data access while eliminating manual handling of disks.
Prices for recordable CD-ROM drives have been dropping steadily, from about $100,000 five years ago to as low as $1,000 today. These devices, from companies such as Plasmon, Ricoh and Sony use laser beams to burn pits in blank disks. The non-erasable disks have low error rates since they are impervious to culprits such as dust, heat or spilled beverages.
Other types of rewritable technology such as magneto-optical systems also are making inroads. New phase-change disks from companies such as NEC and Panasonic enable data rewrites by using stronger laser beams for second and subsequent recordings. These drives are gaining attention because they run a few hundred dollars less than standard recordable devices.
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