ROM

ROM (Read-Only Memory, or sometimes called firmware) is a type of memory which contents are not lost when no electricity and only can be read. ROM on a computer provided by vendor just content programs or data. in the PC it can be called a ROM BIOS (Basic Input / Output System) or ROM BIOS. Instructions in the BIOS is to be run by the microprocessor when the computer start up. processors generally contained in the BIOS are like:

• Checking the contents of CMOS (Compmentary Metal-Oxyde Semiconductor is a type of chip that requires power from the battery).
• Load handling interruptions (interrup handlers) and control devices (device drivers).
• Initialize registers and power management.
• Hardware test (POST or the power-on self-test) to check that all hardware in good condition.
• Display settings on the system.
• Determining the devices to be used to run programs (for example, is hard disk perantinya).
• Taking the contents of the boot sector. Boot sector is a small program by the BIOS this program is loaded into RAM and then the microprocessor will execute the commands existing in the RAM.

example : operating system windows is loaded

source