In computing, ROM stands for "read-only memory" and refers to a type of memory used to store data or information in a permanent form. It is applied mainly in the distribution of firmware and semiconductor integrated circuits.
The contents on ROM are meant to be stored on a permanent basis. This characteristic makes it difficult or impossible to alter or erase the contents stored on ROM. The memory is also nonvolatile, meaning it does not lose its contents when there is no power, unlike random-access memory, better known as RAM, which is volatile. As a result, ROM is the preferred storage for important data such as the basic input output instruction set (BIOS) in computers.
Initially, the contents of ROM could not be erased or altered at all. Technological advancement has led to the development of different types of ROM. There are some that allow the modification or erasure of stored data using special techniques.
Programmable ROM, or PROM, allows only one instance of modifying its contents using high voltage pulses. Erasable PROM, or EPROM, is a type of ROM with content that can be altered several times by exposing it to strong ultraviolet light. Electrically erasable PROM is another type of ROM with contents that can be erased or modified several times electrically.