Optical Storage Devices
• An optical disk is a high-capacity storage medium.
An optical drive uses reflected light to read data.
• To store data, the disk's metal surface is covered with tiny dents (pits) and flat spots (lands), which cause
light to be reflected differently.
• When an optical drive shines light into a pit, the light cannot be reflected back. This represents a bit value
of 0 (off). A land reflects light back to its source,
Representing a bit value of 1 (on)
• In PCs, the most commonly used
Optical storage technology is called
Compact Disk Read-Only Memory (CD-ROM).
• A standard CD-ROM disk can store up to 650
MB of data, or about 70 minutes of audio.
• Once data is written to a standard CD-ROM which causes light to be reflected differently. Disk, the data cannot be altered or overwritten.
Optical Storage Devices - DVD-ROM
• A variation of CD-ROM is called Digital Video Disk
Read-Only Memory (DVD-ROM), and is being used
in place of CD-ROM in many newer PCs.
• Standard DVD disks store up to 9.4 GB of data—
enough to store an entire movie. Dual-layer DVD
disks can store up to 17 GB.
• DVD disks can store so much data because both sides
of the disk are used, along with sophisticated data compression technologies.
This drive lets you record your
own CDs, but data cannot be overwritten once it is
recorded to the disk.
This drive lets you record a
CD, then write new data over the already recorded
This technology is used to store digital photographs.
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