DVD recordable media has two family trees: "Minus-R," which came out first, and "Plus-R." In the first half of the '00s, computers had optical drives that wrote to one type of media or the other. Disks with data on them could be read by drives of either type. "-RW" and "+RW" are the rewriteable versions of each family tree; "-R" and "+R" are writeable, but cannot be erased and rewritten.
History of the Standards
DVD-R was created in 1997 by Pioneer and is vetted by the DVD Forum, the standards body that determines DVD compatibility. DVD+RW was a competing standard promoted by Sony in 2002 made for rewriteable disks, and is maintained by the DVD+RW Alliance, and DVD+R was a secondary standard for nonrewriteable media. Both standards have capacities of 4.7GB; the maximum for DVD-R is 7Kb higher. Both standards allow a disk to be mastered, preventing additional data from being added, effectively "write protecting" it and allowing it to be played in a DVD player. DVD+R initially had greater reliability with unmastered disks, so they were superior for incremental archiving and had faster write speeds. Both of these advantages were later matched by DVD-R.
The "+R" standard uses a different die on the substrate of the disk. DVD+R disks could not be written to in DVD-R drives, and vice versa. In 2006, Apple released computers with SuperDrives, which could write to both media types. By 2007, similar drives were common options on PCs.
DVD Player Compatibility Issues
From 2003 to late 2004, some models of Pioneer DVD player had difficulties reading DVD+R and DVD+RW disks. This problem was fixed by 2005's model year. Both devices can read each other's disks.
Certain computers, such as netbooks, have no optical drives at all, relying instead of flash drives for removable media. Modern computers as of 2012 that do ship with optical drives feature drives that can read and write both formats.
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