Sunday, 25 July 2021

CMOS

What is CMOS?

CMOS stands for Complimentary Metal Oxide Semi-Conductor and it stores roughly 64Kb of data. It is the part of the southbridge in most computers. The specification stored in Complimentary Metal Oxide Semi-Conductor must match hardware and it allows you to access the BIOS. When hardware is change or update, Complimentary Metal Oxide Semi-Conductor must be updated.

CMOS Battery


Accessing BIOS through CMOS setup

Complimentary Metal Oxide Semi-Conductor can only be accessed when the PC is booting and key combination at start-up. The changes are stores on an NVRAM Complimentary Metal Oxide Semi-Conductor chip. The mouse doesn’t work in Complimentary Metal Oxide Semi-Conductor setup.
  • AMI and AWARD BIOS – DEL key 
  • PHOENIX BIOS – CTRL, ALT and ESC keys or F2     

CMOS Chip

Complimentary Metal Oxide Semi-Conductor is stored in an SRAM chip called Non-Volatile Random Access Memory (NVRAM). It stores data that is uses by the BIOS and NVRAM is powered by Complimentary Metal Oxide Semi-Conductor battery. The modern BIOS is stores in EEPROM and EPROM and SRAM means motherboards are updateable. In older motherboards, you can also reset Complimentary Metal Oxide Semi-Conductor. 

Other CMOS Settings

  • Load High Performance defaults 
  • Load BIOS setup defaults 
  • Supervisor password 
  • User password 
  • Disconnect the battery for 1 hour to erase the password! 
  • Complimentary Metal Oxide Semi-Conductor can also be clear using a jumper 

Clear CMOS Jumper

CMOS Jumper 

These jumpers are often located near the BIOS chip itself or next to the CMOS battery. To clear CMOS, move the small plastic jumper from the 2 pins it's on over to the other pins or remove the jumper entirely if this is a 2-pin setup. In a 3-pin setup where the center pin is share. Any confusion here can be clear up by checking the CMOS clearing steps outlined in your computer or motherboard manual.

To confirm, switch on the computer and check through that the BIOS settings have reset, or the system password is now clear or not. If everything is good, shutdown your computer, return the jumper to its original position, and then power on the computer back. If you don't return the jumper to its original position, then CMOS will clear on every restart of your computer.

Caution: Clearing the Complimentary Metal Oxide Semi-Conductor on your motherboard will reset your BIOS settings to their factory defaults.

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