rom

Semiconductor-based computer memory that stores program code that the central processing unit (CPU) can read, but not write to, i.e., change or modify in any way. Programs are stored in ROM on semiconductor chips, also known as firmware or hardware, during the manufacturing process. Such programs are said to be hard-coded to distinguish them from software. The term readonly memory distinguishes it from random access memory (RAM), which also is stored on semiconductors, but is read/write memory. Unlike RAM, ROM is not volatile, i.e., the programs are not lost when the electric power is lost or turned off. Therefore, programs required during system start-up commonly are stored in ROM. Note: Many ROM chips can be reprogrammed after erasing the previous content either electrically or with an external source of ultraviolet (UV) light. See also CPU, firmware, hardware, RAM, semiconductor, and software.