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NOTE: The original Apple SuperDrive (even with older 1.22 firmware)<br />
can write to DVD-RW discs, but not from the iDVD application. You<br />
must use a different software utility, such as Toast, to write to DVD-<br />
RW discs.<br />
DVD-RAM<br />
DVDs and Computers 127<br />
DVD-RAM, with an initial storage capacity of 2.58 billion bytes, later<br />
increased to 4.7, uses phase-change dual (PD) technology with some<br />
magneto-optic (MO) features mixed in. DVD-RAM is the best suited of the<br />
writable DVD formats for use in computers, because of its defect management<br />
and zoned CLV format for rapid access. However, it’s not compatible<br />
with most drives and players (because of defect management, reflectivity<br />
differences, and minor format differences). A wobbled groove is used to<br />
provide clocking data, with marks written in both the groove and the land<br />
between grooves. The grooves and pre-embossed sector headers are<br />
molded into the disc during manufacturing. Single-sided DVD-RAM discs<br />
come with or without cartridges. There are two types of cartridges: type 1<br />
is sealed; type 2 allows the disc to be removed. Discs can only be written<br />
while in the cartridge. Double-sided DVD-RAM discs were initially available<br />
in sealed cartridges only, but now come in removable versions as well. Cartridge<br />
dimensions are 124.6 mm � 135.5 mm � 8.0 mm. DVD-RAM discs<br />
can be rewritten more than 100,000 times, and the discs are expected to<br />
last at least 30 years.<br />
DVD-RAM 1.0 drives appeared in June 1998 (about 6 months late) for<br />
$500 to $800, with blank discs at about $30 for single-sided and $45 for<br />
double-sided. The first DVD-ROM drive to read DVD-RAM discs was<br />
released by Panasonic in 1999 (SR-8583, 5x DVD-ROM, 32x CD). Hitachi’s<br />
GD-5000 drive, released in late 1999, also reads DVD-RAM discs. Blank<br />
DVD-RAM media are manufactured by CMC Magnetics, Hitachi Maxell,<br />
Eastman Kodak, Mitsubishi, Mitsui, Ritek, TDK, and others.<br />
The spec for DVD-RAM version 2.0, with a capacity of 4.7 billion bytes per<br />
side, was published in October 1999. The first drives appeared in June 2000<br />
at about the same price as DVD-RAM 1.0 drives. Single-sided discs were<br />
priced around $25, and double-sided discs were around $30. Disc prices<br />
were under $10 and retail drive prices were under $200 by 2003. DVD-RAM<br />
2.0 also specifies 8-centimeter discs and cartridges for portable uses such<br />
as digital camcorders. Future DVD-RAM discs may use a contrast enhancement<br />
layer and a thermal buffer layer to achieve higher density.
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