Read Only Memory (ROM) is memory that is similar to RAM but that differs in some important regards. Principally, it is non-volatile. If you store information on ROM and remove the power source, the information persists. ROM is commonly used to store programs that the computer needs to access when it boots up. While your hardware components, including your hard drive, may store a great deal of information, the information regarding how to access those devices is commonly stored in the computer’s ROM.
USB flash drives are forms of ROM. Some devices, such as routers and even robots have embedded systems that are held in ROM.