An optical disk storage system consists of a rotating

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Unformatted text preview: llowing purposes: 1. For applications that are based on random data processing. 2. As a shared on-line secondary storage device. Winchester disks and disk packs are often used for this purpose. 3. As a backup device for off-line storage of data so that if by accident, the data on an on-line storage device gets corrupted, it can be retrieved from the backup storage. Floppy disks, zip disks, and disk packs are often used for this purpose. 4. Archiving of data which are not used frequently, but which may be used once in a while. Floppy disks, zip disks, and disk packs are often used for this purpose. 5. Transferring of data and programs from one computer to another, which are not linked together. Floppy disks and zip disks are often used for this purpose. 6. Distribution of software by vendors. Originally sold software or software updates are often distributed by vendors on floppy disks and zip disks. OPTICAL DISK As compared to magnetic tape and magnetic disk, optical disk is a relatively new secondary storage medium. During the last few years, it has proved to be a promising random access medium for high capacity secondary storage because it can store extremely large amounts of data in a limited space. An optical-disk storage system consists of a rotating disk which is coated with a thin metal or some other material that is highly reflective. Laser beam technology is used for recording/reading of data on the disk. Due to the use of laser beam technology, optical disks are also known as laser disks or optical laser disks. Basic Principles of Operation Storage Organization Unlike magnetic disks that have several concentric tracks, an optical disk has one long track that starts at the outer edge and spirals inward to the center (see Figure 8.23). This spiral track is ideal for reading large blocks of sequential data, such as music. But it makes for slower random access time than the concentric tracks used by magnetic disks, whose sectors can be located faster because they are always found on a given track at a fixed distance from the center. Like a track on a magnetic disk, the track of an optical disk is...
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