ROM (an acronym of Read-Only Memory) is semiconductor circuit that contains information that cannot be modified. In the ROM is often recorded the firmware of the technical devices, such as TV, cellular phones, various controllers, or computers.
ROM is also known as Non Volatile Storage since it the information is stored even in the absence of supply voltage. Of course, this definition also includes memory on hard and floppy disks, compact disks, and some other types of memory. However, when speaking about “permanent memory”, it usually means memory devices with arbitrary address access. Such memory devices can be built on different physical principles and have different characteristics not only in terms of capacity and time of access to them, but also, if possible, replacing the information recorded in them.
Classical programmable ROM chips are integrated circuits that physically encode stored data, and therefore after their manufacture it is impossible to change their contents. Nevertheless, special chips are being developed that allow making some changes to the stored information:
- PROM (Programmable read-only memory)
- EPROM (Erasable programmable read-only memory)
- EEPROM (Electrically erasable programmable read-only memory)
- EAROM (Electrically alterable read-only memory)