Which memory is non-volatile and may be written only once?

A programmable read-only memory (PROM) or field programmable read-only memory (FPROM) or one-time programmable non-volatile memory (OTP NVM) is a form of digital memory where the setting of each bit is locked by a fuse or antifuse. It is one type of ROM (read-only memory). The data in them is permanent and cannot be changed.PROMs are used in digital electronic devices to store permanent data, usually low-level programs such as firmware (microcode).