Hardware Reference
In-Depth Information
Thediscisrecordedusing
phase-change recording
,inwhichdataiswrittenbyselectively
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 heat-
ing a spot, which is then rendered less reflective than the remaining crystalline portions.
The signal is read as the difference of the laser reflection rate between the crystalline and
amorphous states. The modulation and error-correction codes are the same as for DVD-
Video and DVD-ROM, ensuring compatibility with other DVD formats. For rewriting, a
lower-powered laser reheats the spot to a lower temperature, where it recrystallizes.
Disc cartridges or caddies originally were required for both single- and double-sided
discs but have now been made optional for single-sided discs and are seldom used today.
Double-sided discs must remain inside the caddy at all times for protection; however,
single-sided discs can be taken out of the cartridge if necessary.
DVD-RAM specifications are shown in
Table 11.13
.
Table 11.13 DVD-RAM Specifications
