Distinguish between ROM, PROM, EPROM, EEPROM.

Ans:

ROM: It also called Read Only Memory is a Permanent Memory. The data is permanently stored and cannot be changed in Permanent ROM. This can only be read from the memory. There cannot be a write operation since the given data is programmed in the device through the manufacturer or the user. It is a Non-volatile memory. Some illustrations of ROM are pre-programmed instructions, conversion tables etc.

PROM: It also called Programmable Read Only Memory permits user to store the data. An instrument PROM programmer is utilized to store the desired data. The process utilized is opening the links at bit locations by using high current (such process is termed as burning in). Once such process has been done, then the data is permanently stored and changes in this impossible.

EPROM: The meaning of this term is Erasable PROM. This can be reprogrammed through first erasing the existing program. EPROM uses N-MOSFET array along with isolated gate structure.  The isolated transistor gate has no electrical link and it can store an electrical charge indefinitely. The data bits in EPROM memory array are represented through presence or absence of charge. Erasure is achieved with removing the gate charge. It can be UV EPROM or EEPROM.

The term UV EPROM implies Ultra Violet Erasable PROM. Erasure is achieved though using ultra violet light. The light passes throughout a window in the IC package to the chip where there are stored charges. Hence the stored contents are erased.

EEPROM: It means Electrically Erasable PROM. In EEPROM memory device, the erasure and programming is done through electrical pulses.