What's inside a computer?
The chipset is designed to control specific computer functions, such as processor and memory interaction, ports control, etc.
There is a special type of ROM chip, called BIOS (Basic Input Output System). The BIOS is responsible for booting the machine. It also contains information about system date and time, hard disk type, etc. A
button battery assures that this information is not erased from the chip when the machine is disconnected.