Definition: CD-ROM drives

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-ROM
   X 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/sec

What 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

A Lot of X's