CD-Rs are rated based on how quickly data can be recorded to them. The original CD-Rs, labeled 1x, were capable of recording at 150 Kilobytes of data per second. The number on newer CD-Rs represent a multiple of that original speed. So 2x CD-Rs can record at 300 KB/second. Most current CD-Rs are 52x, meaning 7,800 KB (or 7.8 MB) of data can be recorded to them per second. Given that most CD-Rs can store 700 MB, at that speed you can burn an entire disc in just under 90 seconds. CD-RW discs are typically capable of recording at much lower speeds, and thus have much lower number values associated with them.