BIOS And CMOS
BIOS Setup | BIOS Functions | Booting Process
CMOS Battery | CMOS Reset
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.
In this article , we will discuss in detail what is BIOS , Functions , Booting Process , BIOS configuration , CMOS Battery , CMOS Reset and other related topics.
BIOS And CMOS
Table Of Contents
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 .
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.
Types Of ROMBIOS
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 :
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 .
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 .
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 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.
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 .