(1) See also 
HD DVR.
(2) (
High 
Definition DVD)  A short-lived, high-capacity optical disc that held four hours of HD video on a single-sided, single-layer 15GB disk.  Sanctioned by the DVD Forum in 2003, HD DVD gave way to Blu-ray within a few years.
Based on the Advanced Optical Disc (AOD) technology from Toshiba and NEC, HD DVD used a blue-violet laser that read pits half the size of a DVD on tracks more tightly packed.  Like Blu-ray, HD DVD supported 1080p resolution and advanced video codecs (see 
H.264 and 
VC-1).  An advantage for media manufacturers was that, unlike Blu-ray, traditional DVD stamping machines needed only minor modifications to make HD DVDs.
The first HD DVD drives were sold in the U.S. in 2006, and Microsoft offered the drive as an Xbox option.  Despite its features and support, in 2008, the majority of movie studios and retail outlets chose Blu-ray over HD DVD, and the "format war" was over.
HD DVD Formats
HD DVD-ROMs were pressed for commercial movies, while HD DVD-Rs were recorded once by the user and HD DVD-RWs were rewritable.  A few dual-format HD DVD/Blu-ray players were developed, and hybrid HD DVD/DVD discs were planned.  See 
Blu-ray, 
HD formats, 
DVD and 
DTV.
 FULL-SIZE HD DVD (120mm) CAPACITIES
         SINGLE SIDED      DOUBLE SIDED
                   HD                HD
 Layers  Storage  Hours    Storage  Hours
 Single    15GB    4       30GB     8
 Dual      30GB    8
 Triple    51GB   14