Phase-change Dual
rewritable optical disc standard
Phase-change Dual (or Phase-change Disc, commonly abbreviated as PD) is a rewritable optical disc format and storage standard introduced by Matsushita Electric Industrial Co., Ltd. in April 1995.
The media offers a capacity of 650 MB on a single side. The discs are 120 mm (4.7 inches) in diameter, identical in size to a standard CD or DVD, and are permanently housed within a protective caddy. PD utilizes phase-change recording technology with a red laser and supports approximately 500,000 rewrite cycles.
Matsushita and other manufacturers produced both internal and external PD drives, which were marketed as a novel "dual function" system capable of reading standard CD-ROMs while also operating as a rewritable phase-change drive. In August 1996, Matsushita integrated the technology into its laptop line by releasing the PRONOTE PD, a notebook computer featuring a built-in drive that functioned as both a 650 MB storage device and a 4× CD-ROM reader.
Technology
The underlying technology of the PD format relies on the phase-change properties of chalcogenide alloys, specifically a GeTe−Sb2Te−3Sb active layer. Chalcogenide compounds are particularly suited for this application because their chain-like bonding structures allow them to easily transition between crystalline and amorphous states.
Data is recorded and read based on the differences in optical properties between these two structural states.
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