Also known as: ROM
Read-only memory (ROM) is non-volatile memory whose contents are written once or rarely and retained without power, traditionally used to hold code a device needs the moment it switches on.1
Overview
Classic mask ROM has its data baked in during manufacture and can never be changed. Later variants made ROM progressively more editable: PROM (programmable once), EPROM (erasable with ultraviolet light), and EEPROM (electrically erasable). Flash memory is the modern, block-erasable descendant of EEPROM and now fills most roles once handled by ROM chips. Despite the name, today’s “ROM” is usually rewritable — but only deliberately, which is the point: it survives power loss and is not casually overwritten like RAM.
Where it fits
ROM’s job is to store the firmware and boot code that bring hardware to life, such as a BIOS/UEFI on a PC or the bootloader on a microcontroller. It is the non-volatile counterpart to volatile RAM: RAM holds the running program and is wiped at power-off, while ROM holds the unchanging instructions that start the machine. In a GopherTrunk capture node, the SDR dongle and the host both rely on firmware held in this kind of memory.
Sources
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Read-only memory — Wikipedia, on ROM, its PROM/EPROM/EEPROM variants, and firmware storage. ↩