The main difference between DVD R and DVD RW is that the R is a write-once format. Data can be burned on the DVD only once. On the other hand, data on an RW disc can be erased and rewritten several times.
Both DVD R and DVD RW come in +/- formats. The essential difference between DVD +/-R and DVD +/-RW remains the same regardless of the + or -.
|DVD R||DVD RW|
|Stands for||Readable only DVD||Readable, Writable DVD|
|Can record files||Only once (i.e. for the very first time), then it is readable only for the rest of its digital life.||Can be written on/recorded on multiple times.|
|Can files be erased?||No||Yes, and new files can be created.|
Write once formats use a single write laser to change a dye layer affecting the opacity of the dye. The laser darkens spots on the recording layer (dye layer) to record information. Rewritable media use a phase change recording layer where the write laser changes the polarization of the recording layer (usually a metallic material) by crystallizing it. In order to erase this layer so new data can be added, an erase laser (usually the recording laser refocused to be wider then that needed to record data) is used. This erasing function heats the layer causing it to become amorphous again as it was in the blank state.