Read Only Memory (ROM)

§  Stores crucial information essential to operate the system, like the program essential to boot the computer.

§  It is not volatile.

§  Always retains its data.

§  Used in embedded systems or where the programming needs no change.

§  Used in calculators and peripheral devices.

§  ROM is further classified into 4 types- ROM, PROM, EPROM, and EEPROM.

Types of Read Only Memory (ROM)

1.      PROM (Programmable read-only memory) – It can be programmed by user. Once programmed, the data and instructions in it cannot be changed.

2.      EPROM (Erasable Programmable read only memory) – It can be reprogrammed. To erase data from it, expose it to ultra violet light. To reprogram it, erase all the previous data.

3.      EEPROM (Electrically erasable programmable read only memory) – The data can be erased by applying electric field, no need of ultra violet light. We can erase only portions of the chip.