Information Technology Reference
In-Depth Information
on the inside. Thus the disk increases its speed progressively as the data is read from the
disk. The actual rate at which the drive reads the data is constant for the disk. The basic
transfer rate for a typical CD-ROM is 150 KB/s. This has recently been increased to
300 KB/s (
×
2 CD drives), 600 KB/s (
×
4), 900 KB/s (
×
6), 1.5 MB/s (
×
10) and even 6 MB/s
(
×
40).
6.9.7 Standards
Data disks are described in the following standards topics, each of them specific to an area or
type of data application. These topics can be obtained by becoming a licensed CD developer
with Philips. These standards apply to media, hardware, operating systems, file systems and
software.
Red Book
World standard for all compact disks (CD-DA) (audio).
Yellow Book
Covers CD-ROM and CD-ROM-XA data formats.
Green Book
Covers CD-I data formats and operating systems (photo).
White Book
CD-I (video)
Orange Book
Covers CD-R/CD-E (CD-Recordable/CD-Eraseable).
Blue Book
CD-Enhanced (CD Extra, CD Plus).
6.9.8 Silver, green, blue or gold
CD-ROMs are available in a number of colours, these are:
•
Silver
. These are read-only disks which are a stamped as an original disk.
•
Gold
. These are recordable disks which use a basic phthalocyanine formulation which
was patented by Mitsui Toatsu Chemicals (MTC) of Japan, and is licensed to other
phthalocyanine media manufacturers. They generally work better with 2m writing speeds
as some models of disk can not be written to at 1m writing speed.
•
Green
. These are recordable disks which are based on cyanine-based formulations. They
are not covered by a governing patent, and are more or less unique to the individual
manufacturers. An early problem was encountered with cyanine-based disk as the dye
became chemically unstable in the presence of sunlight. Other problems included a wide
variation in electrical performance depending on write speed and location (inner or outer
portion of the disk). Eventually, in 1995, some stabilising compounds were added. The
best attempt produced a metal-stabilised cyanine dye formulation that gave excellent
overall performance. Gradually the performance of these disks is approaching gold disk
performance.
•
Blue
. These are recordable disks which are based on an azo media. This was designed
and manufactured by Mitsubishi Chemical Corporation (MCC) and marketed through its
US subsidiary, Verbatim Corporation.
6.10 Magnetic tape
Magnetic tapes use a thin plastic tape with a magnetic coating (normally of ferric oxide).
Most modern tapes are either reel-to-reel or cartridge type. A reel-to-reel tape normally has
two interconnected reels of tape with tension arms (similar to standard compact audio cas-
settes). The cartridge type has a drive belt to spin the reels, this mechanism reduces the strain
