The CD-ROM drive is unlike its floppy and hard drive relatives which reads the data from the disk magnetically. It reads the data by using a laser to scan for the presence or absence of microscopic pits in the disk. The absence of a pit is called a land. Specific combinations of pits and lands represent information.

Like its hard drive relative, the CD-ROM drive comes in IDE or SCSI. Most CD-ROM drives have an IDE and SCSI port built right into the drive. You can connect this drive to the built in IDE port on the motherboard, or the SCSI port on your sound card if you have one.

CD-ROM drives are classified at different speeds. This speed rating refers to the data transfer rate which is how fast the CD-ROM drive can send data to RAM. It is measured in kilobytes per second (KBps). Below is a table listing some CD-ROM drive data transfer rates.

Drive Type	Data Transfer Rate (KB/s)
1X	150
2X	300
3X	450
4X	600
6X	900
8X	1,200
10X	1,500
12X	1,800
16X	2,400
20X	3,000
24X	3,600

A single speed or 1X CD-ROM drive is as fast as your audio compact disc player. The current CD-ROM drives, 16X are sixteen times as fast!

The CD-ROM's access time or the amount of time it takes to find information, ranges between 100-500 milliseconds. The lower the better. A CD-ROM drive is faster than a floppy drive, but slower than a hard drive.

Each CD-ROM disk has a capacity of almost 650MB. This is equivalent to approximately 333,000 pages of typed text, or 74 minutes of music.