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Read only memory

is primary . Its contents are not lost when the computer is turned off.

ROM can be read from, but not written to, hence the term 'read only'. This makes ROM ideal for storing and that are needed for the computer to run. These instructions and data are usually programmed by the computer's manufacturer and cannot be overwritten.

The is an example of a program that is stored in ROM. The BIOS runs as soon as the computer is switched on. It checks that the is functioning correctly, then runs a second program known as the bootup or bootstrap program that loads the computer's from the hard drive into the RAM. The BIOS is always needed so it is stored in ROM.