There are 3 main types of disc.  DVD-Video, DVD-ROM, and DVD-Audio. Each of these DVDs can be in DVD-5, 9, or 10, . The first classification is based on functions and the second classification is based on the capacity or playtime. The names of the DVDs are pretty self-explanatory. DVD-Video is for video, DVD-ROM is for pure data, DVD-Audio is for high quality audio, and DVD-R is the recordable version of all these DVDs. There is also DVD+R which is nothing more than a different kind of recordable disc. Most DVD writers or players do not care whether the recordable media is in + or – format. This used to be a problem some years ago when DVD was quite a new format and certain players would only recognise either the + R discs or the -R discs, but luckily as time has moved on so has the technology and this is no longer a problem.The following table summarizes the different formats of DVDs.Format Capacity Side / Layer Video Playtime CommentDVD-5 4.7 GB Single / Single 2 hours The most basic kind of DVDDVD-9 8.54 GB Single / Double 4 hours Need to be careful during authoring to choose the correct jumping point from Layer-0 to Layer-1.DVD-10 9.4 GB Double / Single 4.5 hours Essentially a DVD-5 on each side. The disc needs to be manually flipped in order to play the other side. No artwork can be printed because both sides contain data.DVD-18 17.1 GB Double / Double 8 hours Essentially a DVD-9 on each side. The disc needs to be manually flipped though and no printing can be done on these discs as both sides contain data.In short the most popular is either a 5 or 9 as niether of these need to be manually turned over and both of these allow data on one side and full colour print on the other.