Hardware Reference
In-Depth Information
used on current products, some recent and current DVD-ROM drives can read DVD-RAM media;
check the specification sheet for a particular drive to verify compatibility.
The first DVD-RAM drives were introduced in spring 1998 and had a capacity of 2.6GB (single-
sided) or 5.2GB (double-sided). DVD-RAM Version 2 discs with 4.7GB capacity arrived in late
1999, and double-sided 9.4GB discs arrived in 2000. DVD-RAM drives typically read DVD-Video,
DVD-ROM, and CD media. Although DVD-ROM drives, older DVD+R/RW and DVD-R/RW drives,
and DVD-Video players can't read DVD-RAM media, DVD Multi and DVD Super Multi drives can
read/write DVD-RAM.
DVD-RAM uses what is called the
wobbled land and groove recording
method, which records
signals on both the lands (the areas between grooves) and inside the grooves that are preformed on
the disc. The tracks wobble, which provides clock data for the drive. Special sector header pits are
prepressed into the disc during the manufacturing process as well. See
Figure 11.13
,
which shows the
wobbled tracks (lands and grooves) with data recorded both on the lands and in the grooves. This is
unlike CD-R or CD-RW, in which data is recorded on the groove only.
Figure 11.13. DVD-RAM wobbled land and groove recording.
The disc is recorded using
phase-change recording
, in which data is written by selectively heating
spots in the grooves or on the lands with a high-powered laser. The DVD-RAM drive write laser
transforms the film from a crystalline to an amorphous state by heating a spot, which is then rendered
