In its normal state the plastic coating is solid

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Unformatted text preview: ook, product catalogs, etc. 3. For distribution of new or upgraded versions of software products by software vendors. 4. For storage and distribution of a wide variety of multimedia applications. 5. For archiving of data, which are not used frequently, but which may be used once in a while. 6. WORM disks are often used by end-user companies to make permanent storage of their own proprietary information. For example, many banks use them for making a permanent record of their daily transactions. MAGNETO-OPTICAL DISK We saw that both CD-ROM and WORM optical disks are permanent storage devices. That is, data once written on them cannot be erased and overwritten. Hence unlike magnetic tapes and magnetic disks, optical disks are not reusable. To overcome this limitation of optical disks, researchers invented magneto-optical disk technology which integrates optical and magnetic disk technologies to enable rewritable storage with laserbeam technology. Since magneto-optical disks are rewritable, they are also known as rewritable optical disks. A magneto-optical disk consists of a rotating disk that is covered with magnetically sensitive metallic crystals sandwiched inside a thin layer of plastic coating. In its normal state, the plastic coating is solid, preventing the metallic crystals from moving. To write data on the disk, the laser beam of greater intensity is focused on the surface of the disk at the location of writing. The intensity of this laser beam is just strong enough to melt the plastic coating for a very short instance of time that is just long enough to allow a magnet to change the orientation of the metaliic crystals. The magnet has an effect at only the point where the laser beam is focused because the plastic coating at only that point is fluid enough to allow the metallic crystals to be reoriented. To read data from a magneto-optical disk, the laser beam of lesser intensity is focused on the disk track formed by the metallic crystals. As the disk spins and the metallic crystals pass under the laser beam, depending on their orientation (alignment), some metallic crystals reflect the light while others scatter the light, produ...
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