To overcome this problem the concept of disk

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Unformatted text preview: tion of the data. For example, primary storage i$ a random access storage. However, this distinction is not always observed strictly and hence disk systems are often referred to as random access storage devices. Disk Formatting Magnetic disks come in various different sizes. The size of a disk is usually referred to by its diameter. Typical disk sizes include those with 14 inch, 9 inch, 8 "inch, 5% inch, 3V4 inch, and VA inch diameter. Obviously, different size disks require different disk drives so that the dimensions of the mechanical components of the disk drive match with that of the disks to be used with it. Even for disks of the same size, all disk drives are not the same because we saw that different computer systems have different ways of organizing data on the disk surface. Hence disk drives of different computers may have their own way of defining tracks, sectors, and sector size (number of bytes/sector) to match their own way of organizing data. This implies that computer manufacturers should also manufacture the disks that can be used in their computer systems. This is a severe limitation because it prevents the use of disks manufactured by third party vendors into one's own computer system. To overcome this problem, the concept of disk formatting was introduced. According to this concept, before a disk can be used with a computer system, it must first be prepared by means of a process called disk formatting by the computer system. For this, the raw (unformatted) disk is inserted in the disk drive of the computer system and the disk formatting command is initiated. In this process, the disk drive's read/write head lays down a magnetic pattern on the disk's surface. This pattern enables the disk drive to organize and store the data in the data organization defined for the disk drive. Most computers maintain on the disk a table with the sector and track locations of data. This table, known as the File Allocation Table (FAT), enables the computer to locate data easily. The disk formatting command also takes care of creating the...
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This document was uploaded on 04/07/2014.

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