Maskable programmable read-only memory (MROM)
- In this type of read-only memory, the user specifies the data to store to the manufacturer of the memory. The data pattern specified by the user programmed as a part of the fabrication process. Once programmed, the data pattern can never change. This type of read-only memory referred to as ROM. ROMs highly suited for very high volume usage due to their low cost.
Programmable read-only memory (PROM)
- This type of memory comes from the manufacturer without any data stored in it, i.e. empty. The data pattern programmed electrically by the user using a special circuit known as PROM programmer. It can programme only once during its lifetime. Once programmed, the data cannot alter. This type of memory is known as PROM. These highly suited for high volume usage due to their low cost of production.
Erasable programmable read-only memory (EPROM)
- In this type of memory, data can write any number of times, i.e. they are reprogrammable. Before it reprogrammed, the contents already stored erased by exposing the chip to ultraviolet radiation for about 30 minutes. This type of memory referred to as EPROM. EPROMs are possible only in MOS technology. Programming is done using a PROM programmer.
Electrically erasable and programmable read-only memory (EEPROM or E2PROM)
- This is another type of reprogrammable memory in which erasing is done electrically rather than exposing the chip to the ultraviolet radiation. It referred to as EEPROM or electrically alterable ROM (EAROM).