Manufacturers express disc capacity in terms of how much computer data a disc can contain. DVD-R (General), DVD-R (Authoring), DVD+R, DVD+RW and DVD-RAM discs come in 4.7 GB single and 9.4 GB double-sided (12 cm) and 1.46 GB single and 2.92 GB double-sided (8 cm) sizes. This has not always been the case for DVD-RAM and DVD-R.