Hardware Reference
In-Depth Information
Chapter 11. Optical Storage
Optical Technology
There are basically three types of disk storage for computers: magnetic,
flash memory
, and optical. In
magnetic
storage, data is recorded magnetically on rotating disks.
Flash memory
, such as SSDs and
flash memory cards, store information in special memory cells that can be written, erased, and
rewritten but retain information when power is turned off.
Optical
disc storage is similar 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
or SSD drives 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 online 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 storage, 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.
At this point, as digital downloads of applications become more popular, the most likely successor to
magnetic storage isn't an optical solution at all, but SSD, which offers speeds faster than hard disk
drives and is steadily increasing in capacity.
Optical technology standards for computers can be divided into three major types:
• CD (compact disc)
• DVD (digital versatile disc)
• BD (Blu-ray disc)
All these are descended from popular music and video entertainment standards; CD-based devices
can also play music CDs, and DVD and BD-based devices can play the same video discs you can
purchase or rent. However, computer drives that can use these types of media also offer many
additional features.
In the following sections, you learn how optical drives and media are similar, how they differ from
each other, and how they can be used to enhance your storage and playback options.
CD-Based Optical Technology
The first type of optical storage that became a widespread computing standard is the CD-ROM. CD-
ROM (
compact disc read-only memory
) is an optical read-only storage medium based on the
original CD-DA (digital audio) format first developed for audio CDs. Other formats, such as CD-R
(CD-recordable) and CD-RW (CD-rewritable), expanded the compact disc's capabilities by making
it writable.
Older CD-ROM discs held 74 minutes of high-fidelity audio in CD audio format or 650MiB
(682MB) of data. However, the current CD-ROM standard is an 80-minute disc with a data capacity
