Explain the purpose of ROM memories in computer systems?

ROM (read-only memory) is a non-volatile memory, so it keeps its contents when the power is off. Its main purpose is to store programs and data that must always be present and need not change. Examples are the bootstrap loader that starts the computer, the BIOS or firmware, and fixed tables such as character codes. The CPU can only read it during normal work. ROM is also used to hold microprograms in the control unit and to implement lookup tables and combinational logic.