Most optical drives today are combo CD/DVD drives that support DVDs and all the CD formats: CD audio, CD-ROM, CD-R and CD-RW. The speeds of the drives are rated by their CD-ROM and DVD transfer rates. The original CD-ROM drive (1x) transferred data at 150KB per second. By doubling the spindle RPMs, the data transfer rate increased to 300KB/sec (2x) and so on. See CD-ROM and DVD drives.CD-ROM CD-ROMX Rating Data Transfer Rate 1x 150 Kilobytes/sec 2x 300 Kilobytes/sec 4x 600 Kilobytes/sec 8x 1.2 Megabytes/sec 10x 1.5 Megabytes/sec 12x 1.8 Megabytes/sec 20x 3.0 Megabytes/sec 36x 5.4 Megabytes/sec 40x 6.0 Megabytes/sec 48x 7.2 Megabytes/sec 50x 7.5 Megabytes/sec 52x 7.8 Megabytes/secWhat Does 40x/12x/48x Mean?CD drive ratings are designated with three speed numbers such as 40x/12x/48x or 40/12/48, as follows:First X / Second X / Third X CD-R write / CD-RW write / CD-ROM read.
Plural form of CD-ROM drive.