DVD Demystified

DVD Comparison
TABLE 8.5
CD-ROM and
DVD-ROM
Specifications
CD-ROM DVD-ROM
Capacity 650.4 MB 4.37 to 15.9 GB
Error correction RS-CIRC RS-PC
Error correction overhead 34 percent 13 percent
Modulation 8/14 (EFM) 8/16 (EFMPlus)
Transfer rate (1�) a 150 KB/s (1.23 Mbps) 1353 KB/s (11.08 Mbps)
Advantages of DVD-ROM over CD-ROM
375
File system ISO 9660, HFS, other UDF, UDF Bridge, ISO 9660, other
aReference rates for single-speed drives. The transfer rate for double-speed drives is 300 KB/s for CD-
ROM and 2705 KB/s for DVD-ROM, and so on.
Capacity. A CD-ROM holds about 650 megabytes. This can be pushed to
about 730 megabytes by squeezing the tracks tighter together. A singlelayer
DVD holds 4.4 gigabytes, which is seven times what a CD-ROM holds.
A dual-layer DVD holds 8.0 gigabytes, 12.5 times more than a CD-ROM. A
double-sided, single-layer DVD holds 8.8 gigabytes, 14 times more than a
CD-ROM. A double-sided, dual-layer DVD holds 15.9 gigabytes, which is 25
times what a CD-ROM holds. (See page 133 for an explanation of the
improvements from CD to DVD that account for the increased capacity.)
Speed. The CD-ROM specification requires a minimum transfer rate of
150 KB/s (150 � 2 10 bytes per second). Memory buffers and multispeed CD-
ROM drives can raise the transfer rate much higher, above that of a singlespeed
(1X) DVD-ROM drive. Multispeed drives spin the disc at higher
multiples of the standard velocity to increase the rate at which data are read
off the CD. However, producers of CD-ROM—based software often must deal
with the installed base of single-speed or double-speed CD-ROM drives.
The DVD-ROM specification requires a minimum transfer rate of 11.08
million bits per second (1353 kilobytes per second), which is nine times
faster than a single-speed CD-ROM drive at 1.23 million bits per second or
roughly equivalent to a 9X CD-ROM drive. As with CD-ROM drives, the
manufacturers will continually increase the speed of DVD-ROM drives to
improve performance. Double-speed and faster DVD-ROM drives came out