READ ONLY MEMORY(ROM)

ROM is also called CMOS (Complementary Metal Oxide Semiconductor) chip. It is an internal memory of a computer which is on a motherboard. It contains BIOS (Basic Input Output System) program which is a bridge between motherboard and operating system. The basic program stored in ROM is called Firmware. The motherboard manufacturer stores the firmware in ROM at the time of manufacturing motherboard. The firmware stored in ROM can only be read by the CPU but can’t be erased or rewritten. so it is called Read Only Memory(ROM).Except the BIOS program,a computer  needs information of devices like keyboard,mouse,hard disk.ram etc each and every time when it is turned on. So, these essential or necessary information are also stored in ROM chip later by the users themselves. These information are not erased when you turned off a computer. Since the program and data stored in ROM do not get erased when the computer is turned off. So it is also called permanent memory or non volatile memory. There are three types of memory:-  
                    
I)PROM(Programmable Read Only Memory)    

II)EPROM(Erasable Programmable Read Only Memory)                                                                     
                                                                                                                                                                        

III)EEPROM(Electrically Erasable Programmable Read Only Memory)