What is the storage type of DVD?

The standard types, just like with the CD format, are:

[ by Format type ]

DVD-ROM (pre-recorded from the factory, OR the "most standard" standard)

DVD-R (the standard blank write-once media)

DVD+R (supposed to offer superior data protection)

DVD-RW (-R rewriteable)

DVD+RW (+R rewriteable)

DVD-RAM (multiple-write sort-of like hard drive/pagefile, supported by certain DVD burners)

DVDs on a PC can be burned either all to DVD-ROM (the default option), or to "physical media type" (DVD-R, DVD+R etc.) - the availability of this latter option depends on the writer hardware and used software.

[ by Content type ]

DVD-Video

DVD-Audio

DVD-Data

[ by Physical Media type (storage space/video or audio length capability etc.) ]

Single-Side, Single-Layer (SSSL, default) - 4.7 GB

Single-Side, Double-Layer (SSDL) - 2x 4.7 GB

Dual-Side, Single-Layer (DSSL) - 2x 4.7 GB

Dual-Side, Double-Layer (DSDL) - 4x 4.7 GB

Also, note that the "video length" and similar information provided on DVDs applies and conforms to reality only, when DVD-Video (or DVD-Audio) format is used, as this forces a pre-defined encoding/compression of information (DVD-Data can store any type of information in any file format).