DVD-RAM

DVD-RAM (DVD Random Access Memory) is a DVD-based disc specification presented in 1996 by the DVD Forum, which specifies rewritable DVD-RAM media and the appropriate DVD writers. DVD-RAM media have been used in computers as well as camcorders and personal video recorders since 1998.

In May 2019, Panasonic, the only remaining manufacturer of DVD-RAM discs, announced that it would end production of DVD-RAM media by the end of that month, citing shrinking demand as the primary motivation. Panasonic made these discs under its own brand name and also under other brands such as Verbatim. The only other manufacturer to produce DVD-RAM discs was Maxell.

The "RAM" in its name is related to random-access memory that computers use as main memory, not in the technology but in sense that it can be used as a random-access memory unit rather than a sequential-access memory unit such as a magnetic tape drive.

DVD-RAM works by means of phase change technology which was chosen instead of magneto-optical technology (an already existing rewritable solution at the time) because it doesn't require a magnetic head and therefore it represented reduced complexity and costs. Phase change technology uses laser light to heat the surface of a phase changing alloy and allows it to go from a crystalline to an amorphous state and vice versa, therefore altering its optical reflectivity index. To change the recording material from a crystalline to an amorphous state, and back again a high or medium power laser light is used to control the rate of cooling of the phase changing alloy therefore establishing the final state. Encoding is done by means of difference in reflectivity of the alloy, a laser is pointed at the surface and the returned intensity signifies either a 1 or a 0.

DVD-RAM uses concentric tracks each divided into hard (factory originated) sectors, in contrast to traditional spiral recording found in other DVD and CD formats. A 12 cm (5") 4.7 GB disc is divided into 35 zones of tracks, with each zone having more sectors per track compared to the previous zone. This makes its data structuring very similar to that of hard drives and floppy disks. This means that usually DVD-RAMs are suitable to be accessed by the OS without any special software

Since the Internationale Funkausstellung Berlin 2003 the specification is being marketed by the RAM Promotion Group (RAMPRG), built by Hitachi, Toshiba, Maxell, LG Electronics, Matsushita/Panasonic, Samsung, Lite-On and Teac. The specification distinguishes between:

Speeds more than 2x are defined by Optional Specifications (Nx-speed DVD-RAM):

DVD-RAM discs can have 12 or 8 cm in diameter, around 5 or 3 inches respectively. The latter variant is mainly intended for camcorders that use DVD as storage media and also exists with capacities of 1.46 GB for a single-sided disc, 2.8 GB for a double-sided disc, and 5.6 GB for a dual-layer double sided disc, however, they are relatively uncommon. DVD-RAMs were originally solely sold in disc caddy cartridges; recent DVD recorders can work with discs either with or without a cartridge, and many devices do not work with cartridges. Discs can be removed from cartridges for use with these drives (except with type 1 media, see table above).