15 in this method the tracks are first partitioned

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Unformatted text preview: 8.14). Thus if there are eight such pie-shaped segments, each track will get divided into eight parts, and each of these eight portions of a track is called a sector. A sector typically contains 512 bytes. A sector is the smallest unit with which any disk can work. That is, disk drives are designed to access (read/write) only whole sectors at a time. Even if the computer needs to change just one byte out of the 512 bytes stored on a sector, it rewrites the entire sector. Notice from Figure 8.14 that the sectors on the outer tracks are longer than those on the inner ones. Since each sector records the same number of characters (usually 512 characters), the length of the sectors on the innermost track determines the storage capacity for the sectors on all other tracks of the disk, This means that the storage space remains underutilized on the sectors in the outer tracks of the disk. This is a disadvantage of dividing disks into pie-shaped segments. To avoid this problem of underutilization of storage space, some systems such as Apple and Commodore, partition the disk in such a manner that all sectors occupy approximately the same amount of space. One such type of partitioning of disk is shown in Figure 8.15. In this method, the tracks are first partitioned into groups, and the tracks in different groups have different number of sectors per track. For example, in Figure 8.15 the tracks are partitioned into three groups. The tracks belonging to the innermost group have 8 sectors per track, the tracks belonging to the next group have 9 sectors per track and the tracks belonging to the outermost group have 10 sectors per track. Using this new method of disk partitioning, Apple was able to increase the storage capacity of its 3 Vi-inch floppy disk by about 40%. When people refer to the number of sectors a disk has, the unit they use is sectors per track - not just sectors. Thus if a disk has 200 tracks and 8 sectors per track, it has 1600 (200 x 8) sectors - not 8 sectors. Each sector of a disk is assigned a unique...
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This document was uploaded on 04/07/2014.

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