Editing Non-volatile memory (section)

=== Read-only and read-mostly devices ===
[[Mask ROM]]s are factory programmable only and typically used for large-volume products which are not required to be updated after the memory device is manufactured. 

[[Programmable read-only memory]] (PROM) can be altered once after the memory device is manufactured using a [[PROM programmer]]. Programming is often done before the device is installed in its target system, typically an [[embedded system]]. The programming is permanent, and further changes require the replacement of the device. Data is stored by physically altering (burning) storage sites in the device.

An [[EPROM]] is an erasable ROM that can be changed more than once. However, writing new data to an EPROM requires a special programmer circuit. EPROMs have a quartz window that allows them to be erased with ultraviolet light, but the whole device is cleared at one time. A [[one-time programmable]] (OTP) device may be implemented using an EPROM chip without the quartz window; this is less costly to manufacture. An electrically erasable programmable read-only memory [[EEPROM]] uses voltage to erase memory. These erasable memory devices require a significant amount of time to erase data and write new data; they are not usually configured to be programmed by the processor of the target system. Data is stored using [[floating-gate transistor]]s, which require special operating voltages to trap or release electric charge on an insulated control gate to store information.