DVD recordable protocols.
  HP originally pushed for the recordable DVD for use as backup media.

  Laser has shorter wavelength (vs. CD-R). 

  DVD disc is actually 1/2 thickness of CD. 
    see wikipedia topic : DVD

  A dummy layer is laminated onto the actual disc to provide stiffness and 
    protection.

  Data actually stored on the lower surface of the real disc (in the middle
    layer).

  Pits/Lands closer together (requiring different dye than cd).

  Writable Discs contain the "wobble" grove for timing and additional 
    pre-written information for better addressability.
 
  DVD-RAM (1996) Good technology - more common in camcorder mini-discs.
    Discs often cartridge mounted mini-discs.
    DVD-RAM is a read/write protocol. (~ $2-$3/disc)
    DVD-RAM has much higher re-write cycle than DVD-RW, 100,000 time at
      low speed, 10,000 times at high speed.

  DVD-R (1997) Original standard supported by most DVD readers.
    DVD-RW (1997) (~ < $1/disc) 
    Rewriteable ~ 1000 times.

  DVD+R (2002) Improved technology allowing for faster reads and more 
    accurate and successful write.
    DVD+RW (1997) but not implemented until 2001 (~ $1 - $1.25 /disc)
    Rewriteable ~ 1000 times.
     

  3 protocols not compatible but incompatibility not at the hardware level,
    so most current computer DVD drives can handle all three protocols. 
  
    Early DVD devices may have problems with non-default protocol.

    Stand-alone recorders, camcorders, and video recorders are often
      protocol specific.

  Both WORM DVDs and Re-writable DVDs provide better longevity than CD-Rs
    and CD-R/Ws

  But environmental protections should be practiced, e.g temperature control,
    humidity control.