A type of non-volatile memory used in computers and electronic devices to store small amounts of data that must be saved when power is removed. Unlike standard ROM, it can be erased and reprogrammed repeatedly using electrical pulses.
Core Characteristics
- Non-Volatility: Data remains intact without power.
- Byte-Addressability: Unlike Flash memory, which must be erased in large blocks, EEPROM allows individual bytes to be read, erased, and rewritten independently.
- Electrical Erasability: It does not require UV light or physical removal to clear; the system can update firmware or data while the chip is still soldered to the circuit board.
- Limited Endurance: While highly reliable, EEPROM has a finite lifespan, typically rated for 100,000 to 1,000,000 write cycles.
Key Terminology
- Floating-Gate Transistor: The fundamental storage cell of an EEPROM. It uses a thin layer of oxide to trap electrons; the presence or absence of charge is represented by 1 or 0.
- Write Cycle: The time required for the chip to clear an existing byte and program a new one. This is generally slower (in the milliseconds range) than RAM.
- Serial vs. Parallel: * Serial EEPROM: Uses protocols like I2C or SPI to communicate, requiring fewer pins (ideal for small devices).
- Parallel EEPROM: Uses a wide data bus for faster transfers but requires a high pin count.
- In-System Programming (ISP): The ability to update the EEPROM’s contents without removing it from its application.
EEPROM vs. Flash Memory
| Feature | EEPROM | Flash Memory |
| Modification Size | Byte-level (precise) | Block-level (bulk) |
| Write Speed | Slower | Faster |
| Capacity | Low (bits to KBs) | High (MBs to TBs) |
| Typical Use | Settings/Configuration | OS/Firmware/Files |
Common Use Cases
- BIOS/UEFI: Storing the low-level firmware and system hardware settings.
- Microcontrollers: Storing user-defined configurations or calibration data in Arduino or IoT projects.
- Identification (SPD): Storing information on RAM modules (DRAM) that tells the motherboard the memory’s speed and timings.
- Consumer Electronics: Saving presets on a car radio, volume settings on a TV, or the “state” of a smart light bulb.
- Security: Storing digital certificates or unique ID keys in credit cards and SIM cards.
Technical Note: Many modern devices use Emulated EEPROM, where a small portion of a larger Flash memory chip is used to act like an EEPROM through software management, reducing component costs.