HP initially developed recordable DVD media from the need to store data for backup and transport.
DVD recordables are now also used for consumer audio and video recording. Three formats were developed: DVD-R/RW(hyphen), DVD+R/RW (plus), and DVD-RAM. DVD-R is available in two formats, General (650 nm) and Authoring (635 nm), where Authoring discs may be recorded with encrypted content but General discs may not.[1]
Although most DVD writers can nowadays write the DVD+R/RW and DVD-R/RW formats (usually denoted by "DVD±RW" and/or the existence of both the DVD Forum logo and the DVD+RW Alliance logo), the "plus" and the "dash" formats use different writing specifications. Most DVD readers and players will play both kinds of discs, although older models can have trouble with the "plus" variants.
Dual-layer recording
Dual-layer recording (sometimes also known as double-layer recording) allows DVD-R and DVD+R discs to store significantly more data—up to 8.54 gigabytes per disc, compared with 4.7 gigabytes for single-layer discs. Along with this, DVD-DL's have slower write speeds as compared to ordinary DVD's and when played on a DVD player, a slight transition can be seen between the layers. DVD-R DLwas developed for the DVD Forum by Pioneer Corporation; DVD+R DL was developed for the DVD+RW Alliance by Philips and Mitsubishi Kagaku Media (MKM).[24]
A dual-layer disc differs from its usual DVD counterpart by employing a second physical layer within the disc itself. The drive with dual-layer capability accesses the second layer by shining the laser through the first semitransparent layer. In some DVD players, the layer change can exhibit a noticeable pause, up to several seconds.[25] This caused some viewers to worry that their dual-layer discs were damaged or defective, with the end result that studios began listing a standard message explaining the dual-layer pausing effect on all dual-layer disc packaging.
DVD recordable discs supporting this technology are backward-compatible with some existing DVD players and DVD-ROM drives.[24] Many current DVD recorders support dual-layer technology, and the price is now comparable to that of single-layer drives, although the blank media remain more expensive. The recording speeds reached by dual-layer media are still well below those of single-layer media.
There are two modes for dual-layer orientation. With Parallel Track Path (PTP), used on DVD-ROM, both layers start at the inside diameter (ID) and end at the outside diameter (OD) with the lead-out. With Opposite Track Path (OTP), used on many Digital Video Discs, the lower layer starts at the ID and the upper layer starts at the OD, where the other layer ends; they share one lead-in and one lead-out. However, some DVDs also use a parallel track, such as those authored episodically, as in a disc with several separate episodes of a TV series—where more often than not, the layer change is in-between titles and therefore would not need to be authored in the opposite track path fashio
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