What is DVD-RW R9 Optical Drive?

DVD+R DL (also called DVD+R9) is a Dual Layer writeable DVD+R.

DVD-R DL (also called DVD-R9) is a Dual Layer writeable DVD-R. The dual layered discs can hold 7.95GB

The dual layered discs (DVD+R9 and DVD-R9) can hold 7.95GB and double sided dual layer (called dvd-18) can hold 15.9GB.