Read-only memory (ROM) is a form of non-volatile computer memory that retains stored data even when the power supply is removed. Its fundamental purpose is to hold critical, fixed information, such as the initial boot instructions (firmware) required to start up a computing device. Unlike volatile memory, which requires constant electrical power to maintain data, ROM architectures are designed for permanent data storage. Various types of ROM exist, differing in how the data is written and whether the data can be erased and rewritten. Early forms were hard-coded and immutable, while later developments introduced programmable or erasable characteristics, allowing systems to update the foundational instructions they rely upon.