Read-Only Memory (ROM) is the earliest non-volatile semiconductor memory. Its core characteristic is that data is permanently solidified once written and will not be lost after power failure, and the original design only supports data reading but not modification. It evolved by rewrite capability into Mask ROM (factory one-time solidified, non-rewritable), PROM (one-time programmable by users), EPROM (erasable by ultraviolet irradiation) and EEPROM (electrically erasable, in-system rewritable). Flash memory, a subsequent derivative, has become its mainstream alternative. Original ROM is now rarely used, mainly applied in scenarios such as early computer BIOS, game cartridges and one-time solidified industrial firmware.