ROM, Read only memory which stores information that can only be read. It is only a type of non-volatile storage means information is maintained even if the component loses power. Once the data is stored on the ROM modifying the data is impossible or very difficult. It contains the basic instruction for what needs to happen when a computer is turned on this referred to as firmware of a computer. Which require the basic code to get computer started and once the computer is up and running the CPU takes over. CD-ROM is another type of ROM which stands for the compact disc read only memory this is also impossible to change.

Types of ROM

PROM

Stands for programmable read-only memory, a type of memory chip on which data can be written only once. Once the program is written it remains there forever. PROMs retain their content when the computer is turned off. Difference between PROM and ROM is that PROM is manufactured as blank memory and ROM is programmed during manufacturing process. To write data on it you required a special device called a PROG programmer or burner.

EPROM

Stands for Erasable programmable read-only memory. This special type of memory retain their content until it is exposed to ultraviolet light which clear its content and making it impossible to reprogram the memory. To write on EPROM and read it you need a special device PROM burner and EEPROM programmer.

EEPROM

Stands for electrically erasable programmable read-only memory. This is the special type of program which can be erase if you expose it electrical charge. Like other types it also retain its content even when the power is turned off.