4.7 GB DVD-RAM Disc

Rewritable DVD-ROM drives, or DVD-RAM, employs phase-change technology with some MO features mixed in rather than the pure optical technology of CD and DVD discs and has its roots in the PD optical disc system. A "land groove" format allows signals to be recorded on both the grooves formed on the disc and in the lands between the grooves. The grooves and pre-embossed sector headers are molded into the disc during manufacturing. The first generation of DVD-RAM products - providing 2.6GB of reusable data space on either side of a disc - first appeared in mid-1998. However, these early drives will be incompatible with the higher-capacity standard, which may use a contrast enhancement layer and a thermal buffer layer to achieve higher density. The specification for DVD-RAM version 2.0 - with a capacity of 4.7 billion bytes per side - was published in October 1999. Hitachi reached the 4.7MB capacity by reducing mark size from 0.41/0.43 microns to 0.28/0.30 microns and track pitch from 0.74 microns to 0.59 microns.