3 a sequential access storage device is one in which

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Unformatted text preview: . Mass storage devices, often referred to as archival storage, are at the bottom of the storage hierarchy. They are cost-effective for the storage of very large quantities of data when fast access time is not necessary. Notice that the use of a hierarchy of storage technologies shown in Figure 8.28, is a cost effective way of designing computer systems with very large storage capacities. Smaller capacity, faster access time, and higher cost per bit stored Cache memory Main memory On-line, direct-access and sequential-access secondary storage device such as hard disk Off-line, direct-access and sequential-access secondary storage devices such as magnetic tape, floppy disk, zip disk, WORM disk, etc. Larger capacity, slower access time, and lower cost per bit stored Mass storage devices such as tape library, CD juke box, etc. Points to Remember 1. The primary storage of a computer system has limited capacity and is volatile. Hence, additional memory, called auxiliary memory or secondary storage, is used with most computer systems. 2. The secondary storage of a computer system is non-volatile and has low cost per bit stored, but it generally has an operating speed far slower than that of the primary storage. 3. A sequential-access storage device is one in which the arrival at the location desired may be preceded by sequencing through other locations, so that access time varies according to location. On the other hand, a random-access storage device is one in which any location in the device may be selected at random, access to the information stored is direct, and approximately equal access time is required for each location. 4. Magnetic tape is the most popular sequential-access storage device. It consists of a plastic ribbon, usually V2 inch or lA inch wide that is coated with a magnetizable recording material. The tape ribbon is stored in reels or a small cartridge or cassette. 5. The tape of a magnetic tape storage is divided into vertical columns called frames and horizontal rows called channels or tracks. A character is recorded per...
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