BIOS stands for Basic Input Output System. The BIOS ( ROMBIOS ) is a system utility program which loads the operating system when computer is switched on. Both BIOS And CMOS work together to load the operating system.


What Is BIOS ?

The operating system is a system software and an essential component of every computer system. The operating system  acts as an interface between computer system hardware and the application programs . And therefore , the  user  cannot  operate the computer system,  till the  time  operating  system  is  completely loaded in to main memory RAM and fully operational .

The CPU ( Central Processing Unit ) is the brain of the computer system. The  CPU’s  first  job  is to locate and  initiate the process of loading the  operating  system,  every time the computer system  is switched  on . This is done with the help of  system  utility program called  BIOS  (  Basic Input Output System  ) .


The  BIOS.  gets activated when computer is powered on . The BIOS ( ROMBIOS ) is a system utility software  that is placed in a ROM chip ( Read only ) on the computer system  motherboard  as  a  firmware . A firmware is software that is embedded into a ROM chip .

The  BIOS  is  the  first start-up  program  executed by  the  CPU – Central Processing Unit when the  computer system  is  switched on . The main job  of the  BIOS  is  to  locate  and  load the operating  system  in  to the  main  system memory  RAM ( Random Access Memory ) .

Functions Of ROMBIOS

The process of loading the computer operating system into the main memory RAM is referred as booting process . The CPU initiates the booting process by invoking the first start-up BIOS program. The BIOS then initiates the booting sequence . The booting  process ends when the operating system is completely loaded into the main memory RAM  and operational .

The main function of the ROMBIOS is to locate and load the  operating system . During the booting process the ROMBIOS needs information such as date , time and other information about user system settings preferences. This information is provided by CMOS .

The  BIOS  performs  following important functions during the computer system   booting process : 

          Functions Of  ROMBIOS

  • To  Check the power supply  to  the computer system.
  • To  check that  essential  internal components such  as  RAM  and  external  peripheral devices are connected  and  working.
  • To  initiate  the  computer  system  booting sequence .
  • To  provide  and load the initial  basic  set of device drivers .
  • To  locate the operating system  and load  into the RAM.
  • To  handover the system control  to the operating system  once  the  OS  is  fully loaded and  operational .

BIOS Features

Computer Operating System

          Features Of  BIOS

  • BIOS – Basic Input Output System.
  • ROMBIOS main Function Is to Load the Operating System.
  • BIOS is Placed Inside ROM Chip Called ROMBIOS.
  • ROMBIOS Also Loads Initial Set Of Drivers.
  • BIOS Chip Is Powered By CMOS Battery.
  • ROMBIOS Configuration Is Saved Due To CMOS Battery.
  • BIOS Finally Handover Control To Operating System.


The BIOS Chip is an essential component placed on every motherboard in a PC . There are many companies that manufacture BIOS firmware chips . Since the BIOS is embedded in a ROM Chip , it is also commonly referred to as ROMBIOS. Some commonly used  types of BIOS brands include  :

  • AMI
  • CMOS
  • WODJ
  • SYXZ

Computer Booting Process

The computer system booting process starts when the user switch on the computer system . The system power supply unit carries out self-test called POST. The “power on self test” checks the computer systems internal hardware for compatibility , connection  and  ensures that no errors exist before loading the operating system .  

Only after  successful completion of the POST ,  the bootstrap loader  routine  on the  BI OS  chip is  invoked  to  load  the  operating  system  . If the POST fails then the computer system  will  beep for different   beep codes .

After successfully completing the POST (  Power On Self Test ) , the BI OS  then  attempt to loads the operating system ( OS )  into the main system memory  RAM  ( Random Access Memory ).

The OS is located either on the internal hard disk  attached to the computer system  OR  from bootable OS disk in the CD ROM drive. The BIOS will pass the control to the operating  system  once  the it  is  fully  loaded .

OS Booting POST
OS Booting POST

Every time you switch on your computer , a message is displayed on your monitor in first few seconds to press a specified key to enter ROMBIOS menu . All computers provide  BIOS /  CMOS  setup utility system program which has a menu-based user interface ( UI ) accessed by pressing a certain key on the keyboard  for  first  few seconds  when the  computer starts.

 Usually the key is displayed on the monitor for short time during the early start up, for example “Press F1 to enter CMOS setup”. The actual key depends on  the  specific computer hardware brand .

BIOS CMOS Configuration Setup

By accessing this CMOS utility program , the user can edit and modify the BIOS configuration settings . The  BIOS  / CMOS  interface  provides the   user  the option to  edit  , modify  the  hardware  configuration  settings  and  save  the changes  made  before  exit  .

Features present in the BIOS setup utility  typically  include  :

The options to configure the hardware components, including setting for their various operating modes and frequencies. For example, selecting how the storage controllers are visible to the operating system.

The user can also  adjust  the  microprocessor ( CPU )  clocking speed ,   Settings for  the System  Clock  and enabling or disabling  the system  components . The CMOS setup gives options  for selecting which devices are potential boot devices, and in which  order  booting   from  them will  be attempted .    


Both ROMBIOS and CMOS work together during the computer booting process . The CMOS is also alternatively referred to as a Real-Time Clock ( RTC ).  The CMOS is a Non-Volatile RAM ( NVRAM ) or CMOS RAM because it retains the stored data even during the computer is switched off . The CMOS stands  for Complementary Metal-Oxide Semiconductor.

The CMOS is placed on the motherboard generally next to ROMBIOS Chip . The CMOS is a  battery powered semiconductor chip ( memory ) inside computer that stores the information needed during the computer booting process. This information includes the system time , date , system hardware settings , user preferences and password  for  your  computer.


How To Reset CMOS ?

The BIOS plays a critical role in booting the computer system . However sometimes  due to some problem , the  BIOS  may  fail  to  boot  the system. And therefore ,  the operating  system  is  not  loaded into the RAM , necessary make the system operational  . In the event of this situation the user cannot operate the computer .

 This can happen due to change of major component  which is incompatible with existing hardware configuration settings . In such situations . the  user can neither   access  the  ROMBIOS  menu  nor he can  operating system . 

If the BIOS is unable to boot the system  due to  hardware compatibility issue or any other  problem then  such problem  can be resolved  by  resetting  the  CMOS. 

CMOS Rest Using Motherboard Jumpers

  • Switch off  the computer system  .
  • Locate the  reset  jumper  on the motherboard  near  the CMOS  battery .
  • Now  place the  jumper pins from first  two  pins  to other two pins to  clear  CMOS   memory  . 
  • Now , set  the jumper back  to the   original  position  on the first  two  pins .
  • This  resets  the  CMOS  memory .
  • The Checksum  Error message will be displayed.
BIOS Reset

We can reset the CMOS memory , by  clearing the CMOS memory and restoring settings back to their factory default state. In most cases, The CMOS memory can be cleared from within the ROMBIOS menu. However , in some cases, this can be done by opening computer’s case and with  the help  of  jumpers on the motherboard , we  can reset  the CMOS  memory .

Some  latest  advanced  motherboards  provide the separate  reset  button   on the motherboard  which  can be used   to  reset  the  BIOS  settings .

CMOS Reset - Removing CMOS Battery

This method is used to clear the CMOS memory when  the motherboard does not have a CLEAR CMOS jumper pins . In this method, the CMOS memory is cleared by removing the CMOS battery .

The CMOS battery provides power to    the  CMOS  volatile memory ( Static RAM ) which  needs constant  power  source  to retain the data  such as current  date , time  and  BIOS settings  values . 

Once the battery is removed , the CMOS memory data will be lost . After some time , the battery is again placed in to the socket thereby restoring the power supply to CMOS memory .

BIOS Reset By Removing CMOS Battery
Removing CMOS Battery Laptop
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