The most common type of non-volatile memory is the ROM device. This device is read only and the data is masked into the chip during manufacture. Variations of the ROM are one off programmable ones (PROM), erasable ones (EPROM) using UV light, electrical erasable ones (EEPROM). These devices allow the user to blow them with programs and re-program if incorrect. As engineers we will often use the EPROM version, the pinning details are shown below

The internal structure of the EPROM is similar the SRAM, but does not require a write pin; it employs light sensitive fuses to hold the data.

The actual device has a window in it, this enables the device to be cleaned using UV light, usually this window is covered up to prevent slow eraser by normal light.