The DVD-R format was one of the first formats for DVD to hit the market and was created by Pioneer in autumn of 1997. Because the format has been around for a while pretty much anything that will read a DVD, will read a DVD-R.

What does this mean for you? Basically nothing... There really aren't any differences between the DVD-R vs DVD+R that you will ever notice. Now, with that being said, Let's discuss the situations where you will exclusively want to use a DVD-R.

If you are planning on making home made movies or making a copy of your newly purchased DVD so you can watch the copy instead of the original, (So you can keep your original away from those angry DVD monsters called kids and pets...) Then you will want to use a DVD-R. The reason for this is purely due to the fact that DVD-R has been around for so long that it is recognized in nearly 98% of all DVD related players. It's a compatibility thing.

If you have a newer (2003 or later) dvd player and you don't plan on taking your movies to your parents house who were the first ones to pick up a DVD player, then you can just use the DVD+R.

The DVD+R format was introduced somewhere around mid 2002. The biggest differences between the DVD+R vs DVD-R is: there are less burn errors on a DVD+R and the format is newer, DVD+R's can be burned faster than DVD-R. Otherwise, the two formats do exactly the same thing.

If you haven't read about the DVD-R, I suggest you do so if you plan on burning movies.

Since there really aren't any differences between the DVD-R vs DVD+R, it doesn't make a hill of beans as to which ones you pick up. Just make sure that your DVD Burner will support both formats. Older DVD burners will only burn to the DVD-R format but all of the newer burners will burn to both.

The DVD-RW and DVD+R formats (I will refer to them as: DVD±RW) formats are very similar to the CD-RW format (except for the amount of data a DVD±RW can hold compared to CD-RW.)
The purpose of the DVD±RW formats is the ability to burn data to the disc, more than once. You can burn a DVD±RW, erase the information on it, then burn different or more information to it. Kind of like the old Floppy Disks.

So who needs a DVD±RW disc? Anyone who has information that is constantly being changed or added to. These formats are great for business individuals because they can purchase one or two DVD±RW discs and just keep writing to it (1000+ times). This cuts down on the cost of continually buying DVD±R discs which can only be burned once.

The DVD-RAM format is quite a bit different from the DVD±R and DVD±RW format. First of all, the DVD-RAM is more like the DVD±RW than the DVD±R in the sense that it can have files added to it as well as taken away.

Why would I buy a DVD-RAM if I can do the same thing with a DVD±RW? The technology behind the DVD-RAM is completely different than the DVD±R and DVD±RW which use a dye to store the information. When the laser hits the unburned dye, it creates a divit or crater within the dye of the disc and this crater is the binary / digital version of the old vinyl records. DVD-RAM works on the same principle except it doesn't use a dye. It uses a thin piece of metal with 'switches', much like a light switch. When the laser runs across the switch, it is either on or off, creating the binary 1's and 0's. Because the media itself is metal instead of a dye, it has a much longer shelf life (30+ yrs) compared to the DVD±R or DVD±RW (between 10 and 15 years).

Who needs to use the DVD-RAM format?
Mainly businesses or individuals who want to store information for a long time, without worrying about the DVD media being messed up. If a regular DVD±R or DVD±RW is kept in a climate controlled environment, the shelf-life should be much longer but there still aren't any guarantees.