What is the Connection Between EEPROM and Flash?

G.W. Poulos

Electronically Erasable Programmable Read Only Memory (EEPROM) and flash memory have much in common. Both EEPROM and flash memory are built on a chip format, can store data that can be erased and rewritten, and use the same floating-gate transistor technology. While it is correct to state that flash memory is a type of EEPROM, the terms EEPROM and flash memory usually describe different devices.

Flash is typically used with USB devices.
Flash is typically used with USB devices.

EEPROM, in general terms, refers to any type of data memory device that can have digital data written to it and erased through use of an electronic device of some type. This is in contrast to Erasable Programmable Read Only Memory (EPROM), which must be physically removed and erased via a non-electronic method, such as with ultraviolet light. As the write and erase executions of flash memory are performed with a computer, flash memory is, by definition, EEPROM.

Even though flash memory is a type of EEPROM, the two terms usually describe very different types of devices. For example, EEPROM is typically incorporated into a larger integrated circuit (IC). It serves the function of storing various pieces of data that the rest of the IC needs in order to accomplish its purpose. EEPROM does this by storing data in small blocks, usually only a single byte in length.

Flash memory, on the other hand, typically sees use in stand-alone memory storage devices, such as USB drives or camera memory cards, and stores computer user files. To do this, the data is organized into large blocks, each containing many bytes of data. These large blocks can be accessed and erased much faster than single-byte blocks of data. This far greater speed in handling data is where flash memory derives its name.

EEPROM and flash memory both use floating-gate transistors to store data. As a result, both forms of memory are non-volatile. Non-volatile refers to memory that can continue to store data even when there is no power available. This is in contrast to other types of memory, such as computer random access memory, that dump all stored data as soon as power is removed.

Another shared attribute of floating-gate transistor based technologies is the limited life cycle of the transistors due to a phenomenon called memory wear. Each time data is written or erased from these devices, a little more wear occurs. Eventually, after 10,000 to 100,000 cycles, the transistors will begin to fail. While EEPROM contains operational data that seldom changes, data stored on flash memory is often changed. Therefore, while both EEPROM and flash memory experience memory wear, it typically has a much greater effect on flash memory.

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