Repairing and Upgrading Your PC

Optical Drive Performance

Optical drive speeds are specified using an "X-factor." The earliest CD-ROM drives transferred data at a constant 150 KB/s, the same rate used by audio CDs, which is referred to as 1X. Later CD drives used variable speeds, changing the speed according to where the head was positioned on the CD. It's impossible to assign a single speed rating to such a drive, so manufacturers began specifying the maximum speed those drives used. For example, a CD-ROM drive that transfers data at a maximum rate 52 times the 150 KB/s audio CD rate, or 7,800 KB/s, is called a 52X Max drive.

DVD drives use the same kind of speed rating scheme, but the DVD "X-factor" is different. The 1X DVD rate is 1.321 MB/s, which is the data rate required to store 60 minutes of video on a 4.7 GB DVD disc, or about nine times faster than a 1X CD-ROM drive. For example, a 16X Max DVD drive transfers data as fast as about 21 MB/s, nearly three times the rate of a 52X CD drive.

To complicate matters further, optical drives do different tasks at different rates. For example, a typical early CD writer could write CD-R (write-once) discs at 4X, or 600 KB/s, but read discs at 24X, or 3,600 KB/s. When CD-RW (rewritable) discs were introduced, yet a third number was needed, because most CD writers wrote CD-R discs and CD-RW discs at different speeds. A typical modern CD writer might read CD discs at 52X, write CD-R discs at 52X, and rewrite CD-RW discs at 32X. Such a drive is referred to as a 52-52-32 ...