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All you need to know
about CDs and DVDs
LIKE MANY TECHNICAL PRODUCTS, CDs and DVDs can be confusing. What
do those plus (+) and dash (-) symbols mean? What’s the best format to use
for certain projects? Here’s a look at how optical disc technology works.
How optical disc technology works
Compact discs (CDs) and digital video discs (DVDs) generally come in
two choices: recordable (R) and rewritable (RW).
Recordable discs can be written to only once because marks are “burned”
into the disc with a laser during the writing process. As a laser passes over the
disc during the reading (playing) process, it reads a zero when hitting one of
these burned marks and a one when the laser hits an area of the disc that was
not burned. These zeros and ones are referred to as “bits,” or binary digits, and
are the basis for digital technology—the technical way information is stored.
With rewritable (RW) discs, the marks are not “burned” into the disc.
Once a mark is made on the disc, the laser has the ability to change or reverse
the mark. This is why these discs can be overwritten multiple times.
Choose discs according to your applications
It is highly recommended that you back up files, whether they are photos,
videos or documents. CDs and DVDs can safeguard your data in case of a
catastrophic loss, such as when a hard drive crashes.
The amount of data that you want to back up will determine how many
discs you need. The chart at right shows the capacities of today’s most popular optical discs. CDs store 700 MB (736,819, 200 bytes) and DVDs can store
4. 7 to 8. 5 GB ( 1 GB equals 1 billion bytes). The newest format, Blu-ray Disc™
media, can store an amazing 25 to 50 GB.
If you want to back up the hard drive on your computer, RW discs are a
good choice because they can be reused. On the other hand, R discs are more
CLEANING OPTICAL DISCS
• Gently wipe disc with a soft, dry lint-free
cloth, commercial CD cleaner or ethyl alcohol.
• Always wipe in a straight line from the
center of the disc out, in radial fashion.
