/roʊm/
noun … “Non-volatile storage for permanent instructions.”
ROM (Read-Only Memory) is a type of non-volatile memory used to store data or program instructions that must persist even when the system is powered off. Unlike volatile memory such as RAM, contents of ROM are typically fixed at manufacturing or written once and rarely modified. ROM is commonly used to hold firmware, bootloaders, and essential system-level instructions required to start and initialize hardware.
Key characteristics of ROM include:
- Non-volatility: retains data permanently without power.
- Limited write capability: often written once (e.g., mask ROM) or modified through specialized processes (e.g., EEPROM, flash ROM).
- Bootstrapping: contains critical instructions that allow a system to initialize hardware and load an operating system.
- Reliability: less prone to accidental modification or corruption compared to volatile memory.
- Integration: frequently embedded in motherboards, embedded devices, and microcontrollers.
Workflow example: During system startup, the CPU reads instructions from ROM to initialize hardware components and configure memory before transferring control to the operating system loaded into RAM:
-- Simplified boot sequence
cpu.fetch("ROM:Bootloader")
bootloader.initialize_hardware()
bootloader.load_os("RAM")Conceptually, ROM is like a sealed instruction manual permanently attached to a machine. No matter how many times the machine is powered off and on, the manual is always available to guide its startup and operation.
See Memory, RAM, Flash Memory, Firmware, CPU.