Hardware Reference
In-Depth Information
Chapter 11. Optical Storage
Optical Technology
There are basically two types of disk storage for computers: magnetic and optical. In
mag-
netic
storage,dataisrecordedmagneticallyonrotatingdisks.
Optical
discstorageissimilar
to magnetic disk storage in basic operation, but it reads and writes using light (optically)
instead of magnetism. Although most magnetic disk storage is fully read and write capable
many times over, many optical storage media are either read-only or write-once. Note the
convention in which we refer to magnetic as
disk
and optical as
disc
. This is not a law or
rule but is followed by most in the industry.
At one time, it was thought that optical storage would replace magnetic as the primary on-
line storage medium. However, optical storage has proven to be much slower and far less
dense than magnetic storage and is much more adaptable to removable-media designs. As
such, optical storage is more often used for backup or archival storage purposes and as a
mechanism by which programs or data can be loaded onto magnetic drives. Magnetic stor-
age, being significantly faster and capable of holding much more information than optical
media in the same amount of space, is more suited for direct online storage and most likely
won't be replaced in that role by optical storage anytime soon.
Optical technology standards for computers can be divided into three major types:
• CD (compact disc)
• DVD (digital versatile disc)
• BD (Blu-ray disc)
All of these are descended from popular music and video entertainment standards; CD-
baseddevicescanalsoplaymusicCDs,andDVDandBD-baseddevicescanplaythesame
video discs you can purchase or rent. However, computer drives that can use these types of
media also offer many additional features.
Inthefollowingsections,youwilllearnhowopticaldrivesandmediaaresimilar,howthey
differ fromeach other,andhowthey can beused toenhance yourstorage andplayback op-
tions.
CD-Based Optical Technology
The first type of optical storage that became a widespread computing standard is the CD-
ROM. CD-ROM, or
compact disc read-only memory
, is an optical read-only storage me-
dium based on the original CD-DA (digital audio) format first developed for audio CDs.
