The memory which is programmed at the time of its manufacturing is

ROM is written once during manufacture and holds fixed data thereafter.

RAM is written and rewritten freely by the running computer, not fixed at manufacture.

PROM is blank at manufacture and programmed later by the user, once.

EPROM is user programmable and can be erased with ultraviolet light.

The masked contents of ROM cannot be changed after production.

ROM commonly stores the firmware needed to start the machine.