BIOS and CMOS

ROM chips on a computer motherboard contain programs which allow the central processing unit to communicate with the keyboard, drives, and other devices. RAM is cleared when a PC is rebooted, but ROM is not. The programs on the ROM chip are called the Basic Input / Output Services or BIOS.


When a PC boots up, it first loads the BIOS program, then looks for the video card BIOS to activate the monitor, then loads hard disks with a separate BIOS program. A device check is performed for the keyboard and memory. Then the CMOS chip will be referenced to see which device should be booted from - a DVD, flash drive, or hard drive - which will contain an operating system to use.


Because some devices used with a PC can be reconfigured (unlike a keyboard), the uneditable BIOS software on the ROM chip has to work with its own RAM chip, that is readable and writable, the Complementary Metal Oxide Semiconductor (CMOS). A CMOS has its own battery (usually one of those lithium cell batteries that car key fobs use) because it will lose its contents after the PC is shut down if doesn't have power. Other devices will have drivers or software the operating system will load to acces them, or have their own BIOS chips. CMOS RAM chips will contain the system clock for a PC


CMOS data can be accessed while a PC is starting up, and the data can be edited. It's possible to deactivate particular devices connected to the motherboard, or change the settings for the processor. A BIOS password can be set to add an extra security feature for a PC. If a CMOS battery is removed, this password will also be removed along with all of the CMOS data.


Before Windows 8, a PC operating system would bring up BIOS settings when F1, F2, or F10 was pressed while the PC was booting up. In Windows 10, it's possible to access BIOS settings by going to Settings . . . Update & Security . . . Recovery, and clicking 'Restart now' in the Advanced Startup section. Then in the new reboot menu go to Troubleshoot . . . Advanced options. Under the UEFI Firmware settings, you'll see the option to restart and go into BIOS.


Look for the password settings in the security or password section of the BIOS utility.