EPROM stands for Erasable Programmable Read-Only Memory. It is a type of programmable read-only memory chip that retains its data when its power supply is switched off. EPROMs are easily recognizable by the transparent fused quartz (or on later models resin) window on the top of the package, through which the silicon chip is visible, and which permits exposure to ultraviolet light during erasing.

EPROM technology was first developed at Intel in 1971 by Dov Frohman. He based his invention on the idea that the floating gate of a metal-oxide semiconductor field-effect transistor (MOSFET) could be used for the cell of a reprogrammable ROM. To program the EPROM, a high voltage is applied to the control gate, which causes electrons to move through the oxide layer into the floating gate. The floating gate impedes the subsequent operations of the control gate.

EPROMs have a limited but large number of erase cycles; the silicon dioxide around the gates accumulates damage from each cycle, making the chip unreliable after several thousand cycles. EPROM programming is slow compared to other forms of memory. However, EPROMs are still used for programs designed for repeated use but that can be upgraded with a later version of a program.

EPROMs are being increasingly replaced by EEPROM for small sizes, where the cell cost isnt too important, and flash for larger sizes. EEPROM stands for Electrically Erasable Programmable Read-Only Memory. It is a type of non-volatile ROM that enables individual bytes of data to be erased and reprogrammed. EEPROM can be erased and programmed electrically, and most EEPROM chips have a life span of 10,000 to 100,000 write cycles, which is considerably greater than the write cycles of EPROM chips.