Every modern personal computer utilizes electronic circuits to hold data and instructions. RAM is volatile, and is primarily used for the temporary storage of programs that are running. ROM is non-volatile, and usually holds the basic instruction sets a computer needs to operate. Electronic medium is susceptible to static electricity damage and has a limited life expectancy, but in the modern personal computer, electronic hardware usually becomes obsolete before it fails. Optical storage medium, on the other hand, will last indefinitely.
Optical storage is an increasingly popular method of storing data.
Optical disk drives use lasers to read and write to their medium. When writing to an optical disk, a laser creates pits on its surface to represent data. Areas not burned into pits by the laser are called lands. The laser reads back the data on the optical disk by scanning for pits and lands. At the factory, lasers are used to create a master CD-ROM, and a mold is made from the master and used to create copies.