Broadly speaking, there are two types of discs you can record on, a blank disc which can be recorded onto once, or a disc which can be recorded onto multiple times. Generally speaking, a re-recordable disc costs more than a one time recordable disc.

DVD-Video

Can hold upto 135 minutes of images. It has mpeg-2 compression and Dolby digital surrounding. Dual layered discs can produce distortion occasionally.

DVD+R and DVD-R

The +R/-R means that the disc can only be recorded onto once.

DVD+RW and DVD-RW

The +RW/-RW means the disc is re-recordable. They are random access, so no finalisation is required at the finish of a recording.

Significance of "-" and "+"

The "-" and "+" symbols has little significance, other than, they are compatible with different manufacturers. For example, Sony usually support the "-" technology. The "-" and "+" technologies were developed by different manufacturers during DVDs inception. There are slight differences between the two formats.

Capacity

The following DVD versions can store differing amounts of data.

DVD-1 -------- 1.46 gigabyte
DVD-2 -------- 2.66 gigabyte
DVD-3 -------- 2.92 gigabyte
DVD-4 -------- 4.7 gigabyte
DVD-5 -------- 5.32 gigabyte
DVD-9 -------- 8.54 gigabyte
DVD-10 ------ 9.4 gigabyte
DVD-14 ------ 13.24 gigabyte
DVD-18 ------ 17.08 gigabyte

As you can see, the format number closely correlates the amount of data (in gigabytes) that a disc can hold.

SL stands for 'single layer', meaning the discs can be recorded on one side. DL stands for double layer, which means the discs can be recorded on both sides.

DVD-R SL ------- 4.71 gigabyte
DVD-R DL ------- 8.54 gigabyte
DVD+R SL ------ 4.70 gigabyte
DVD+R DL ------ 8.55 gigabyte

As you can see there is only a slight difference in storage capacity between +R and -R discs.