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Unformatted text preview: nyl jacket that is harder than the disk itself but is still flexible. As shown in Figure 8.19, the jacket has on oval cutout (aperture) through which the read/write head makes direct contact with the disk surface. It moves radially along this opening of the jacket cover. The disk has a hole in the center in which the drive's spindle fits so that the disk can be rotated at high speed during operation. The disk rotates inside its jacket cover whose inner side is smooth and permits free rotation of the disk. Early 5'/4-inch floppy disks recorded data on only one side of the disk and were known as single-sided (SS) diskettes. However, today all 5'A-inch diskettes use both the disk surfaces for data recording and are known as double-sided (DS) diskettes. The doublesided 5%-inch diskette of today come in two capacities - double density (DD) and high density (HD). Recall that disk density refers to the number of bits that can be stored per square inch area on one surface of the disk. The DSDD (double-sided, double-density) 574-inch diskettes have 40 tracks, 9 sectors/track, and 512 bytes/sector, giving a total disk storage capacity of 2 (for two surfaces) x 40 x 9 x 512 = 3,68,640 bytes = 360 KB (approximately). On the other hand, the DSHD (double-sided, high density) 5V4-inch diskettes have 80 tracks, 15 sectors/track and 512 bytes/sector, giving a total disk storage capacity of 2 x 80 x 15 x .512=12,28,800 bytes = 1.2 MB (approximately). 2. The 3 ½ -inch diskette. It is a floppy disk of 3 '/2-inch diameter. The disk is encased in a square hard-plastic jacket cover. The jacket cover has a cutout (aperture) for the read/write head to make contact with the disk surface. However, unlike the 5'/4-inch diskettes, this aperture of the 3'/2-inch diskettes is covered with a sliding metal piece (see Figure 8.20). When the diskette is inserted into the drive, this covers slides back to expose the disk surface to the read/write head. Light indicator (blinks when read/write operation takes plac...
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This document was uploaded on 04/07/2014.

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