Microsoft Office Tutorials and References
In Depth Information
Storage Media
Figure 11
Inside a hard disk drive
Optical storage devices are polycarbonate discs coated with a refl ective metal on
which data is recorded using laser technology as a trail of tiny pits or dark spots on the
surface of the disc. The data that these pits or spots represent can then be “read” with a
beam of laser light. Figure 12 shows how data is stored on optical media.
Figure 12
How data is stored on an optical disc
Areas that are not
pits or darkened have
a reflective surface.
When a DVD or
CD-ROM disk is
manufactured, a laser
burns pits or creates
dark spots in the
reflective surface.
These pits become
dark, nonreflective
areas of the disc.
disc
reflective cover
protective
plastic coating
When the laser strikes a
reflective surface, light
bounce s back into the
read head. The patterns of
dark spots and light spots
represent data.
When the DVD or CD-ROM drive
reads the data on the disk, it uses
a laser beam. When the beam
strikes a pit or a darkened spot,
no light is reflected.
A compact disc ) is an optical storage device that can store up to 700 MB. A DVD , CD (
though the same size as a CD, is an optical storage device that stores between 4.7 and
15.9 GB of data, depending on whether data is stored on one or both sides of the disc and
how many layers of data each side contains. A DVD capable of storing 4.7 GB of data
has more than enough storage capacity for an entire feature-length fi lm—up to 9 hours
of video or 30 hours of CD-quality audio. The term “DVD” is no longer an acronym,
although it was originally an acronym for “digital video disc” or “digital versatile disc.”
Blu-ray discs store 25 GB of data per layer. They are used for storing high-defi nition video.
To store data on a CD, you need to record it on a CD-R compact disc recordable ) (
or CD-RW compact disc rewritable ) drive and a CD-R or CD-RW disc. CDs that you (
buy with software or music already on them are CD-ROMs compact disc read-only (
Optical storage media
are very durable but not
indestructible. Take care
not to scratch the disc
surface or expose it to
high temperatures.
 
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