The Read Only Memory (ROM) is a non-volatile memory whose memory content is stored during the manufacturing process and cannot be changed or deleted. The ROM content is retained even after the operating voltage is switched off. ROMs are therefore used for storing programs and data that must be available to the central processing unit continuously and unchanged.
The memory chip developed in 1971 is programmed by the manufacturer. This programming is usually done with the last metallization mask and cannot be changed afterwards. This manufacturing process allows memory chips to be prefabricated down to the last metallization step. Subsequent modification of the stored data is not possible.