DVD Demystified

DVD Comparison
TABLE 8.9
MO and DVD-ROM
Specifications
the disc. A high-power laser is used to heat spots that are changed by a local
magnetic field.
Essentially, two standard formats of MO discs and drives exist. The 3.5inch
format first appeared with 128 megabytes of capacity, moved up to 230
megabytes, and recently became available in 640-megabyte sizes. The 5.25inch
format currently is available in 1.2- and 2.6-gigabyte capacities. The
2.6-gigabyte version holds 1.3 gigabytes on each side of the disc.
Proprietary versions of MO drives can store as much as 4.6 gigabytes,
but these do not follow the ISO standards. Although they can read discs
from other drives, their high-density formatted discs do not work in other
drives. Table 8.9 lists MO specifications.
Advantages of DVD-ROM over MO
393
Cost. A 3.5-inch MO drive costs $500 to $700, with blank cartridges
priced around $30. The 5.25-inch drives cost around $2000, with blank discs
in the $40 to $60 range. DVD drives and discs, including blank writable
discs, are cheaper, and prices continue to drop.
DVD discs can be stamped quickly and cheaply. MO discs generally are
not used for prerecorded data because they are expensive and must be
recorded individually.
Capacity. DVD-ROM discs hold much more than MO discs. Writable
DVD discs hold 4.7 billion bytes, more than the largest standard MO disc.
The next generation of MO technology is expected to have storage capacities
of about 7 billion bytes per side, close to the 8.5 billion bytes of duallayer
DVD-ROM discs, although writable DVD is not available in dual-layer
form. MO development has slowed down considerably since recordable
DVD was released.
MO DVD
Capacity (10 �) 128M bytes to 2.6G bytes 4.7 to 17G bytes
Sector size 512 or 1024 bytes 2048 bytes
Transfer rate a (2 �) Up to 3.9 MB/s 1.3 MB/s
a Reference rates for single-speed drives.