Chapter 12. DVD Drives
DVD originally stood for
Digital Video Disc, later for Digital
Versatile Disc (yuck), and now officially stands for
nothing at all. DVD is basically CD on steroids. Like a CD, a DVD
stores data using tiny pits and lands embossed on a spiral track on
an aluminized surface. But where CD-ROM uses a 780 nanometer (nm)
infrared laser, DVD uses a 636 nm or 650 nm laser. Shorter
wavelengths can resolve smaller pits, which enables pits (and tracks)
to be spaced more closely. In conjunction with improved sector
formatting, more efficient correction codes, tighter tolerances, and
a somewhat larger recording area, this allows a standard DVD disc to
store seven times as much data—about 4.7 GB for DVD versus
about 650 MB for CD-ROM.
One significant enhancement of DVD over CD is that DVD does away with
the plethora of incompatible CD formats. Every DVD disc uses the same
physical file structure, promoted by the Optical Storage Technology
Association (OSTA), and called Universal Disc
Format (UDF). This common physical format means that, in
theory at least, any DVD drive or player can read any file on any DVD
disc. Microsoft did not support UDF until Windows 98. This forced DVD
content providers to adopt an interim standard called UDF
Bridge, which combines UDF and the CD standard ISO 9660.
Only Windows 95 OSR2 and later support UDF Bridge, which forced DVD
hardware manufacturers to include UDF Bridge support with their
hardware in order to support pre-OSR2 Windows 95 versions.
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