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A
typical CD-ROM (Compact Disk-Read Only Memory) disk
holds 650 Megabytes, which is equivalent to 471
floppy disks. Video, graphics and sound are easily
stored. Unlike a floppy or storage diskette, CD-ROMs
are 'read only'. A special drive called a CD-R or
CD-RW is required to write data on a CD. CD-ROM
drives work much like a audio CD player. A laser
reads tracks and sectors accessing data. Audio and
MPEG movies CDs can also be played from a regular
CD-ROM drive.
CD-ROM drives are rated by how fast they can
transfer data from the disc to the system. The
original CD-ROM drive transferred data at 150kbps
(kilobytes per second). They were referred to as
single-speed drives because they operated at the
same speed as audio CD players. Double-speed or 2X
CD-ROM drives transfer data at 300kbps, or two times
the speed of the original. All CD-ROM drives are
compared to the original single-speed drive.
Compatibility
is also very important when choosing a CD-ROM
drive. A good CD-ROM drive is able to read a minimum
of the following formats: CD-DA, CD-ROM/XA, CD-I/MPEG, Photo CD, Karaoke CD, CD-Extra (CD+),
I-TRAX CD, CD-RW, Packet write.
Constant Linear Velocity (CLV)
- The spin rate of the CD increases and decreases as
the drive reads data from different parts of the
disk, achieving constant transfer rates. A CD-ROM
drive reads data from a CD at the same speed whether
it is reading the inside (beginning) of the CD or
the outside (end) of the CD.
Constant Angular Velocity (CAV) - Data is read at
variable speeds while the CD spins at a constant
speed. A 32X MAX / 12X MIN rating means that the CD
will constantly run at 12X while data is read at 32X
or as needed. The advantages of this technology
include less power consumption, and higher maximum
transfer speeds than comparable CLV CD-ROM drives.
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