“Dual Layer” is the term used for DVD-ROM media that has two layers but is one sided, meaning that the laser adjusts itself to read through one layer to read the next.
“Double layer” is the same thing, only its the term that the DVD RW Group uses for their dual layer technology. Its the same thing - just a different take on the name. Maybe they trademarked it. The disc holds 8.5GB across the two layers.
“Double sided” media are basically two single layer discs stuck together with the write layers exposed. This is the kind of disc you have to flip: 4.37 GB each side.
Any drive can write double sided media, because its just single layer media. The user just needs to take the disc out and flip it over. Its no different than two single layer discs.
Dual layer (or “Double Layer” as you’ll most likely see on the packaging) media can only be written by certain burners. You will see that they advertise support for “DVD+R DL” or “double layer” media. These drives include the NEC ND-2510A, NEC ND-3500A, Lite-On SOHW-832S, Sony DRU-700A, HP 530i, TDK 1616, Pioneer DVR-A08/DVR-108, and others.