An emerging technology that many expect will have a profound impact on mass storage strategies in the 1990s is the optical disk. With this technology, laser beams write and read data at incredible densities, thousands of times finer than the density of a typical magnetic disk.
Data are placed onto optical disks with high-intensity laser beams that burn tiny holes into the disks’ surface.
Then a lower-intensity laser beam reads the data inscribed. Optical disk systems have recently started to become widely used on microcomputer systems, which, until recently, did not have mass storage available to them.
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Most optical disk units are of the CD-ROM (Compact Disk-Read Only-Memory) type; that is, you buy a prerecorded disk and “play” (read) it on the optical disk unit attached to your computer. You cannot write new data to the disk in any way.
There are also systems available that will let you write once to the disk; once written, the data cannot be erased. These are called WORM (Write Once, Ream Many) disk systems. Since optical disks have very large storage capacities, most users can write to the disk for a year or more before using it up.
Optical disk systems that allow you to erase unwanted data have also recently become available.
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Today 5.25 inch optical disks can store almost 1 gigabyte of data. Roughly translated, that’s close to 1 million pages of text or, alternatively, the contents of approximately 2.500 diskettes.
So-called optical jukeboxes, which offer online access to hundreds of optical disks, also have become available. These devices can store close to 300 billion bytes of data. Despite the excitement over optical disks, hard disks still have two very important advantages.
First, hard disks are much faster; 10 to 15 times faster is not unusual. Second, there’s a lot of software around written for hard disks that will have to be modified to work on optical disks.