Dual-layer recording (sometimes also known as double-layer recording) allows DVD-R and DVD+R discs to store significantly more data—up to 8.5 gigabytes per disc, compared with 4.7 gigabytes for single-layer discs.[22] Along with this, DVD-DLs have slower write speeds as compared to ordinary DVDs. When played, a slight transition can sometimes be seen in the playback when the player changes layers. DVD-R DL was 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).[23]
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.[24] 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.[23] 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.
Dual layer DVDs are recorded using Opposite Track Path (OTP).[25] DVD-ROM discs mastered for computer use are produced with track 0 starting at the inside diameter (as is the case with a single layer). Track 1 then starts at the outside diameter. DVD video discs are mastered slightly differently. The video is divided between the layers such that layer 1 can be made to start at the same diameter that layer 0 finishes. This speeds up the transition as the layer changes because although the laser does have to refocus on layer 1, it does not have to skip across the disc to find it.
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.[24] 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.[23] 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.
Dual layer DVDs are recorded using Opposite Track Path (OTP).[25] DVD-ROM discs mastered for computer use are produced with track 0 starting at the inside diameter (as is the case with a single layer). Track 1 then starts at the outside diameter. DVD video discs are mastered slightly differently. The video is divided between the layers such that layer 1 can be made to start at the same diameter that layer 0 finishes. This speeds up the transition as the layer changes because although the laser does have to refocus on layer 1, it does not have to skip across the disc to find it.
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