Digital Versatile Disk Random Access Memory (storage) (DVD-RAM) Rewritable DVD media that is recordable on both sides, giving up to 9.6GB of storage. A drive can record to disk and read from it at the same time, so the term full duplex is often used. There are two general types of media: traditional discrete disk in DVD or Jewel case, and one in a permanent case like a large floppy; the disk remains in the case, and the case goes into the drive. The former can sometimes be read by regular DVD drives; the latter obviously cannot.
Technical details, somewhat dated, at burnworld.com. Last updated: 2005-01-26
