The CD-Rom is a disk that hold text, audio and other digital information in small separated pieces kept on the surface so it can be easily scanned and retrieved. An optical laser is used at 780nm on the disk as it spins . When the laser hits depressions in the disk, called pits, it causes a drop in the laser's signal and each drop is called a bit. The information is actually stored according to the length of the bit . The bits, versus land (non-depressed disk section), create an on/off pattern that translates into 1 and 0 respectively .