To know the real performance of a CD or DVD unit is not as simple as it seems. Even though optic units usually have their performance printed on their front panels, such performance is not real.

The performance of CD units is usually informed through the number of times the unit is faster than the standard CD player. The transfer rate of the standard CD Player is 150 KB/s. Thus, a 52x unit has a maximum theoretical performance of 52 x 150 KB/s = 7,800 KB/s.

The transfer rate of the standard DVD Player is 1,350 KB/s. Thus, a 4x DVD-ROM unit has a transfer rate of 4 x 1,350 KB/s = 5,400 KB/s.

Note that the speed measurement unit used on CD-ROM’s is different from the unit used on DVD-ROM’s. A 1x speed in a DVD unit equals to a 9x speed in a CD.

The problem is that both CD and DVD units operate with constant angular speed (CAV, Constant Angular Velocity). In plain English, that means that the speed informed by the manufacturer is only obtained when the unit is reading the data at the border of the disc. When it is reading the data from the innermost part of the disc, the unit usually reaches half its nominal speed. That is, when it is reading the innermost sectors, a 52x unit usually operates at a 26x rate!

In other words, the maximum speed of a CD unit, which is what all of us use to choose which unit to buy, is often incorrect, for there is a performance difference among same speed units from different manufacturers.

To know the real performance of your CD or DVD unit, download the program CD Speed or DVD Speed, both available at To execute the program, you will need a “full” CD-ROM, that is, one having nearly 650 MB of data. The program will read all the sectors of the CD, displaying a graph while it does so. After finishing the tests, the program will inform which is the true speed of your CD-ROM unit, that is, it average speed. Besides the speed, the program also show other quite interesting pieces of information on your optic unit, such as the time it takes it to recognize a CD and the time it takes it to open and to close the tray. In other words, to know the average speed of a CD unit is more important than knowing its maximum speed.

Measuring CD-ROM PerformanceFigure 1: Measuring your CD-ROM real performance.