What is ROM and its Types

Read Only Memory [ROM]

This type of primary memory can only be read but cannot be written. This is a non-volatile memory i.e. its content remains maintained even if power supply is discontinued. Content of ROM is fully embedded on the ROM chip.

Some of ROM do allow to change their content through some special devices but again once changed, their content cannot be overwritten directly by users. ROM is also random access in nature that means processor can access its content from any location.

Types of ROM

Programmable ROM (PROM): PROM stands for Program. Mable Read-Only Memory. Unlike a ROM chip, initially a PROM chip comes from the manufacturers without any programming written on it. An end user can write program on it through a device called a PROM programmer, which uses high voltages to permanently destroy or create internal links within the PROM chip. As it can be written only once, so it is also called one-time programmable (OTP) ROM.

Erasable Programmable Read-Only Memory (EPROM): It is different from PROM because it can be programmed more than once. An EPROM programming is erased only through exposure to strong ultra violet light. The EPROM is configured or reconfigured using a special device called EPROM programmer.

Electrically Erasable Programmable ROM (EEPROM): An EEPROM is like an EPROM chip since it can be written in or programmed more than once. Its content can be electrically erased, and then rewritten electrically. Unlike the EPROM chip, an EEPROM chip need not be taken out of the computer or electronic device of which it is part, when a new program or data needs to be written on it.