Whereas the MO disc adopts the magneto-optical recording system, the DVD-RAM(rewritable) DVD disc will adopt the phase-change recording system. One reason is that the reading method for a disc recorded by the phase-change system is the same asthat for a CD and a read-only(CD-ROM and DVD-ROM) DVD disc, and therefore it is easy to achieve compatibility with them.

Another advantage of this system is that a two-sided disc can be easily realized because both writing and reading can be executed by a single pickup. Moreover, because both data deletion and writing are executed simultaneously, disc rotation at data rewriting is just once, unlike with a conventional MO disc, thereby enabling high-speed data rewriting. Storage density and data transfer speed are both three times faster than for MO discs. Furthermore, great expansion of capacity and speed will be possible in the future.

With the phase-change recording system, data reading and writing are executed by changing a compound from the crystalline to the amorphous phase. By irradiating a strong laser on a writing side coated with the compound which is initially in a crystalline phase, the compound is heated to a high temperature and is changed to an amorphous phase for recording.

In contrast, the magneto-optical recording system used for MO discs utilizes magnetic characteristics. Data is recorded as magnetic poles (S pole and N pole) of magnetic substances in the disc. The current standard requires the disc to be rotated at least twice for data deletion and writing, and this constrainsthe writing speed. Also, structurally, the standard is not suitable for two-sided discs.

* Figures used for comparison are as of April 1996.