Magnetic tape is a typical example of a sequential

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Unformatted text preview: ration of monthly pay slips, or monthly electricity bills, etc., where most, if not all, of the data records need to be processed one after another. In these applications, data records for each and every employee or customer needs to be processed at scheduled intervals (in this case monthly). However, while working with a sequential-access device, if an address is required out of order, it can only be reached by searching through all those addresses which are stored before it. For instance, data stored at the last few locations cannot be accessed until all preceding locations in the sequence have been traversed. This is analogous to a music tape cassette. If 10 songs are recorded on a music tape and if you want to listen to (or access) the 8th song, you must listen to the 7 songs that come before your favorite song before you can hear it. Although your player may "fast forward" the tape quickly past the first 7 songs, the first 7 songs are still accessed although not fully played. In the same way, to access the 28th data record stored on a sequential-access device, the computer must first access (although not process) the first 27 data records. Magnetic tape is a typical example of a sequential-access storage device. In many applications, we need to access information in a more direct manner than sequential-access devices allow. For example, in a computerized bank, at any instance it is required to determine the exact balance in the savings account of a particular customer. Similarly, in a computerized airline ticket booking system, immediate access may be required to reservation system records to find out if seats are currently available on a particular flight. In such applications, if we use a sequential-access device for data storage, the time taken to access the desired information may be enormous which will cause frustration to the customer. Secondary storage devices exist which permit access to individual information in a more direct or immediate manner. These direct-acc...
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This document was uploaded on 04/07/2014.

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