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 700 MB for CD-ROM versus about 4.7 GB for DVD.
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.