EPROM (Erasable Programmable Read-Only Memory) and EEPROM (Electrically Erasable Programmable Read-Only Memory) are both non-volatile memory technologies that retain data without power. While they share similarities, their internal architectures, erasure mechanisms, and use cases differ significantly. This article explores their technical distinctions, operational workflows, and real-world applications.

2. What is EPROM?

Definition:
EPROM is a reprogrammable memory chip that requires ultraviolet (UV) light for erasure.

Key Features:

• Structure:

• Contains a grid of floating-gate transistors.

• A transparent quartz window allows UV light to reach the silicon die for erasure.

• Erasure Process:

• Entire chip must be exposed to UV light (wavelength ~253.7 nm) for 10–30 minutes.

• Requires physical removal from the circuit.

• Programming:

• Uses a high-voltage programmer (12–25 V) to inject electrons into floating gates.

• Endurance: ~1,000 erase/write cycles due to UV-induced oxide degradation.

• Applications:

• Firmware storage in early microcontrollers, BIOS chips, and prototypes.

• Largely obsolete today but still used in legacy systems.

Pros:

• Lower cost per bit compared to early EEPROM.

• Non-volatile and stable for long-term storage.

Cons:

• Slow erasure process.

• Inability to erase individual bytes.

3. What is EEPROM?

Definition:
EEPROM is a reprogrammable memory that uses electrical signals for erasure and writing.

Key Features:

• Structure:

• Similar floating-gate transistors but with an additional control gate for selective erasure.

• No quartz window; fully encapsulated.

• Erasure Process:

• Erased and reprogrammed in-circuit using voltages (e.g., 5 V or 12 V).

• Supports byte-level modifications.

• Programming:

• Electrons tunnel through a thin oxide layer (Fowler-Nordheim tunneling).

• Endurance: ~10,000 to 100,000 cycles, limited by oxide wear.

• Applications:

• Storing configuration data (e.g., calibration settings, passwords).

• Widely used in IoT devices, automotive systems, and consumer electronics.

Pros:

• Selective erasure and in-circuit reprogramming.

• Faster and more convenient than EPROM.

Cons:

• Higher cost per bit historically.

• Slower write speeds compared to RAM.

4. Key Differences

5. Technical Evolution

• EPROM dominated in the 1970s–1980s but was phased out due to operational inefficiency.

• EEPROM emerged in the 1980s, enabling field updates and smaller form factors.

• Flash Memory (a type of EEPROM) later replaced both for high-density storage by using block-level erasure.

6. Practical Considerations

• Choose EPROM if:

• Developing low-cost legacy systems with infrequent updates.

• Choose EEPROM if:

• Requiring frequent, partial data updates (e.g., sensor calibration).

• Modern Alternatives:

• Flash for large-scale storage (e.g., SSDs).

• FRAM or MRAM for high-endurance applications.

Conclusion

EPROM and EEPROM revolutionized embedded systems by enabling reprogrammable non-volatile storage. While EPROM’s UV erasure made it suitable for prototyping, EEPROM’s electrical erasure paved the way for modern in-field updates. Today, both remain relevant in niche applications, though newer technologies like Flash and MRAM dominate mainstream use.