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Unformatted text preview: split up into sectors, but
with optical disks each sector has the same length regardless of whether it is located near
the disk's center or away from the center. This type of data organization allows data to be
packed at maximum density over the entire disk. However, it also requires a more complicated drive mechanism because the rotation speed of the disk must varv inversely
with the radius; the drive must slow down the disk's rotation speed to read sectors
towards the outside of the disk and speed it up to read sectors towards the center of the
(a) Track pattern on an optical disk
(b) Track pattern on a magnetic disk
The cost-per-bit of storage is very low for optical disks because of their low cost and
enormous storage density. They come in various sizes ranging from 12-inch to 4.7-inch
diameter. The most popular one is of 5.25 inch diameter whose capacity is around 650
Megabytes. This storage capacity is equivalent to about 2, 50,000 pages of printed text or
total capacity of 550 double-sided, high-density floppy disks of the same size. This
tremendous storage capacity makes optical disks the most suitable storage media for
multimedia applications (described in Chapter 19).
As optical disks have a single track, their storage capacity depends on the following:
1. Number of sectors, and
2. Number of bytes per sector
It is a multiple of the above two parameters. That is,
Storage capacity of an optical disk = Number of sectors
x Number of bytes per sector
The 5.25-inch optical disks typically have 3,30,000 sectors, each of 2352 bytes. That
gives a total capacity of 3,30,000 x 2352 = 776 x 10 6 bytes = 776 Megabytes. This is the
unformatted capacity. The formatted capacity is about 650 Megabytes.
Optical disks use laser beam technology for recording/reading of data on the disk surface.
With this technology, the read/write head used in magnetic storage is replaced by two
laser beam sources. One laser beam (of greater intensity) is used t...
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This document was uploaded on 04/07/2014.
- Spring '14