Formats

Not unlike the different flavours of CDs, there are five physical formats, or books, of DVD:

• DVD-ROM is a high-capacity data storage medium
• DVD-Video is a digital storage medium for feature-length motion pictures
• DVD-Audio is an audio-only storage format similar to CD-Audio
• DVD-R offers a write-once, read-many storage format akin to CD-R
• DVD-RAM was the first rewritable (erasable) flavour of DVD to come to market and has subsequently found competition in the rival DVD-RW and DVD+RW format.

With the same overall size as a standard 120mm diameter, 1.2mm thick CD, DVD discs provide up to 17GB of storage with higher than CD-ROM transfer rates and similar to CD-ROM access times and come in four versions:

• DVD-5 is a single-sided single-layered disc boosting capacity seven-fold to 4.7GB
• DVD-9 is a single-sided double-layered disc offering 8.5GB
• DVD-10 is a 9.4GB dual-sided single-layered disc
• DVD-18 will increase capacity to a huge 17GB on a dual-sided dual-layered disc.

The first commercial DVD-18 title, The Stand, was released in October 1999. However, given how long it took for production of dual-layer, single-sided discs to become practical, it is difficult to forecast how long it'll be before the yields of DVD-18 discs will meet the replication demands of mainstream movie distribution, especially since low yields mean higher replication costs. It's likely that a DVD-14 format - two layers on one side, one layer on the other side - will be seen in the interim, since they're somewhat easier to produce.

It is important to recognise that in addition to the five physical formats, DVD also has a number of application formats, such as DVD-Video and DVD-Audio. The Sony PlayStation2 game console is an example of a special application format.