CD-ROM drives

CD-ROM drives, which today typically means a CD-RW drive that is a combo CD-ROM, CD-R and CD-RW drive, come in a variety of speeds. The original drive (1x) transferred data at 150KB per second. By doubling the spindle speed (RPMs) for 2x drives, the transfer rate increased to 300KB/sec and has been increasing ever since. See CD-ROM and DVD drives.

      X        Data Transfer
      Rating   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 Do 40/12/48 or 40x/12x/48x Mean?
CD-RW drives have three speeds that are designated with three numbers or sometimes three "X" numbers; for example, 40/12/48 or 40x/12x/48x." The numbers are write/rewrite/read speeds.

    First X     /  Second X     /  Third X
    CD-R write  /  CD-RW write  /  CD-ROM read

A Lotta X's

This is the label from a Memorex combo CD and DVD drive in 2005. Each "X" number means the speed for that format is X times 150KB for CDs and X times 1.35MB for DVDs.