Difference between PROM, EPROM, and EEPROM?

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Detailed Solution

The main difference between PROM, EPROM, and EEPROM lies in their programmability, reusability, and erasing methods. These are all types of non-volatile ROM (Read-Only Memory) used to store firmware or permanent data in digital devices.

Key Differences

Feature	PROM	EPROM	EEPROM
Full Form	Programmable Read-Only Memory	Erasable Programmable Read-Only Memory	Electrically Erasable Programmable Read-Only Memory
Programmability	Programmable only once; cannot be modified later	Can be erased and reprogrammed multiple times	Can be erased and reprogrammed multiple times electrically
Erasing Method	Not erasable	Erased using ultraviolet (UV) light	Erased using electrical signals
Reusability	Cannot be reused once programmed	Reusable after UV erasure	Fully reusable; supports selective byte/block erasure
Speed	Fast read, one-time write	Fast read, slower erase and write	Moderate read/write speed, faster erase
Program Cycle Lifetime	1-time write	100–1,000 cycles	Up to 1,000,000+ cycles
In-Circuit Update	Not possible	Not possible (requires removal for UV erasure)	Possible; can be erased and written in-circuit
Typical Use	Permanent firmware or device configuration storage	Early microcontrollers, BIOS updates during testing	Modern devices like BIOS chips, microcontrollers, and sensor memories