ROMs

ROM stands for read-only memory, a non-volatile form of computer memory that permanently stores data. Unlike RAM, ROM retains its contents when power is removed, making it suitable for firmware and other essential software that must be available at boot or reset.

ROM technologies encompass a range of approaches. Mask ROM is pre-programmed at manufacture. PROM is programmable once with a PROM programmer. EPROM can be erased and reprogrammed using ultraviolet light. EEPROM and flash memory are electrically erasable and reprogrammable, with flash memory dominating bulk storage in many devices. These variations differ in cost, speed, density, and how often they can be rewritten.

ROM is non-volatile but generally slower and less flexible than writable memory. It is primarily used to store firmware, bootloaders, and fixed software in computers, consumer electronics, and embedded systems. In personal computers, the system firmware (BIOS or UEFI) resides in ROM or flash memory. Embedded devices such as routers, microcontrollers, and appliances rely on ROM-stored code to start and operate.

In emulation and software preservation contexts, the term ROM can also refer to a ROM image, a digital copy of the contents of a cartridge or device’s read-only memory. While ROM images support preservation and accessibility, distributing copyrighted ROMs may infringe rights holders, and legality varies by jurisdiction and use case.

ROMs thus play a foundational role in powering hardware with stable, unchanging software across a wide range of devices, from early computers to modern embedded systems.