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In-Depth Information
1.4.4 Future Trends
Current tape media technology has a physical limitation relative to the partic-
ular process or magnetic coating in use for the last 10 years or so. It is believed
that a new media formulation will be required to allow tape to exceed 16 TB
per cartridge. Tape capacity is increasing at a rate of about 40% per year.
1.5 Optical Storage
Optical storage looked very promising in the 1980s and 1990s. The new
method of storage promised very large capacities and fast access methods
in its early years. After two decades, it is apparent that the technology has a
definite niche with its most popular formats, the compact disc (CD) and dig-
ital versatile disc (DVD), primarily suited for storing music and videos. The
major benefit of optical storage today is its wide acceptance in the commer-
cial marketplace and low cost. Optical drives are found on nearly every new
computer and function particularly well as read-only media. Unfortunately,
the technology was never able to achieve the write access rates or capacities
that would allow it to compete with magnetic storage. Optical storage media
is an order of magnitude behind magnetic storage in available capacity and
transfer rates. 7
1.5.1 CDs
The smallest unit of data on compact discs is called a frame, and discs capable
of storing 650 MB have tracks with pitches (distance between tracks) of 1.6
μ
m. As the track pitch gets closer together, the CD can hold more data,
but the ability of drives to read the CD decreases. The highest-capacity CDs
today hold 700 MB or slightly more and have track pitches of 1.5
m. Data
rate in writing to CDs is determined by the speed of the drive used, which
is represented by the factor of improvement over a baseline (1x) performance
required for digital audio playback at 44 KHz. Data rates of modern CDs have
leveled off around 48x-52x on writing (48-52 times faster than the baseline
rate), which yields a sustained data transfer rate of around 7-9 MB/s. The
archival life of CDs is not comparable to magnetic storage either inasmuch as
each CD lasts typically 5-7 years before data is at risk. Due to the relatively
short archive life, slow transfer speeds, and small capacity in comparison with
magnetic storage, the technology is not in use in high-performance computing
or mass storage system environments.
μ
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