What is ROM?

ROM is stand for Read only memory is a type of main memory that holds special type of a small amount of software called BIOS (Basic Input Output System) that is responsible to start up your operating system. ROM is nonvolatile memory means it hold contents/data without power supply. Phonix and America megatrands are two main manufacturer of ROM. There are three types of ROM. PROM(Programmable Read Only Memory). Special type of ROM that can be programmed using special type of a software. EROM(Erasable Read Only Memory) The type of PROM that can be alter using ultraviolet. EEROM(Electrically Erasable Read Only ROM) 

can be alter using Electric charge.