Dvd9 holds 8.5Gig (7.95 in real space) Commercial dvds are Dvd9. Dvd5 is your standard blank Dvd which is 4.7Gig. (4.38 in real space) Though Dual Layer blank Dvd's are available at more exspense.
Dvd5 - single layer, approx. 4.7gb of data (actually closer to 4464mb of data), burn speeds up to 16x. Dvd9 - dual layer, approx. 8.4gb of data (actually closer to 7900mb), burn speeds up to 6x. Edit: per Mr. Ryan's info.
DVD 5 discs are discs that have a single recording layer on the bottom half of the 2-piece disc. (All DVDs come in two pieces--a recording half on the bottom and a dummy cover on top. There are technical reasons for this.) These discs hold about 4,470 MB of data, but since a "thousand" in computer terms has to be a binary form of 2, that "thousand" is actually 1,024; so the multiple in GB is 4.7, optimistically rounded up to 5. DVD 9 discs are discs that have two recording layers on the bottom half. The numbers end up being about 7,900MB or 8.5GB, rounded up to 9 even more optimistically. The reason that the two layers do not double the 4.7GB is that the pits on the discs are increased by about 10% to make it easier for the laser to read through the outer layer into the inner layer. The majority of movie discs are DVD 9 for two reasons: more room to store data allows less compression for better picture quality and extra features on the disc, and Hollywood did not expect anyone to develop a double-layer disc so their two layers would make it harder for people to copy. The DVD5/DVD9 designation applies mostly to movie discs (known as DVD-ROM discs or "replicated" discs despite the fact that they are actually digital duplicates, not analogue replicas--apparently no one in the naming conventions studied philology!) There are no double layer rewritable discs except JVC's DVD-RW DL that requires all new software, drives, and players. It's a flop, as expected.
Deffinately JoeRyan takes the cake. What I tred to post was blown out the water by Mr. Ryan's sage advice.
