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What is BIOS?

A screenshot of a BIOS configuration screen.
A computer motherboard.
A CMOS chip, which holds the information BIOS needs to start.
Article Details
  • Originally Written By: RR
  • Revised By: G. Wiesen
  • Edited By: L. S. Wynn
  • Images By: Aaron Parecki, Via Gallery, Ing_Masa
  • Last Modified Date: 19 July 2014
  • Copyright Protected:
    2003-2014
    Conjecture Corporation
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A Basic Input/Output System (BIOS) is an electronic set of instructions that a Personal Computer (PC) uses to successfully start up. It is located on a chip on the motherboard inside of a computer and is designed to be protected from disk failure. While it can be updated, this should be done carefully to avoid damaging the computer or leaving it unable to start up. Certain computer manufacturers, such as Apple™, use other systems like Open Firmware.

The Function of BIOS

One of the main functions of the BIOS is to give instructions for the Power-On Self Test (POST). This self test ensures that the computer has all of the necessary parts and functionality needed to successfully start itself, such as use of memory and a keyboard and other components. If errors are detected during the test, the computer gives a code that reveals the problem. Error codes are typically presented as a series of beeps heard shortly after startup.

The BIOS also works to give the computer basic information about how to interact with some critical components, such as hard drives and memory, needed to load the Operating System (OS). Once the basic instructions have been loaded and the self-test has been passed, the computer can proceed with loading the OS from one of the attached drives. Functions and control over hardware within the computer are then handed over to the OS and it controls the system afterward.

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How It Is Stored on a Computer

Traditional BIOS firmware is included on a computer motherboard as Read Only Memory (ROM). This means that the system is accessible but is not dynamically written to the way that a computer's hard drive is during operation. A battery on the motherboard keeps the data on it intact, even when the computer is turned off while not in use. Although sometimes confused with a Complementary Metal Oxide Semiconductor (CMOS), the BIOS refers to the firmware on the motherboard while the CMOS is the physical location where the date and system configuration data are stored.

Many PC manufacturers today use flash-memory to hold this system, which allows users to more easily update it on computers. This can solve problems with the original BIOS or add new functionality to it. Users can periodically check for new versions, as some vendors release numerous updates over the course of a product's lifetime. To find an update, users should check the manufacturer of their motherboard. These updates should be done carefully, however, as incorrect versions or corrupted software can make a computer impossible to start up.

Configuring and Controlling the BIOS

PC users can make certain adjustments to the system through a configuration screen on the computer. The setup screen is typically accessed with a special key sequence during the first moments of startup, often "Delete" or a Function key. This setup screen allows users to change the order in which drives are accessed during startup, monitor computer component temperatures, and control the functionality of a number of devices. Most computer users never need to access these systems on their computer, though many fixes to simple errors can require adjustments.

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Discuss this Article

anon333840
Post 38

What is the relationship between BIOS, CMOS and POST?

anon313752
Post 36

My PC isn't getting past the POST checks. All the motherboard LEDs light up, the HDD spins up and so does the CPU heatsink fan. Help.

anon285295
Post 34

When my computer is booting up after being turned on, this message appears on the screen:

"Invalid configuration information - please run SETUP program.

Performing automatic IDE configuration

Primary Master: Disk Drive

Secondary Master: CD-ROM Device

Secondary Slave: CD-ROM Device

Time of day not set - please run SETUP program"

What should I do to resolve this problem and not see this message every time I turn on my computer?

anon285294
Post 33

What should I do to resolve this problem and not see this message every time I turn on my computer?

anon259600
Post 31

I'm having some problems with my college's assignment. I really need to know what is the definition of adding input/output instructions, so please do help me.

anon135867
Post 28

I can't finish system recovery. Computer says my recovery disk 3 is not good. Recovery from HDD = error 1002. Then dos says BOOTMGR is missing Press Ctrl+alt+ del to restart. over and over again. What can i do to fix this?

anon115864
Post 26

my windows xp is freezing up after i installed a new defender pro internet security software from wally mart but it won't let me view any programs to remove it. when i click on add remove programs it's blank. help?

anon103623
Post 24

and mine says: sometimes no keyboard detected, sometimes cmos battery low,and overclocking failed.

anon98783
Post 23

my name is diallo and i have a problem with my laptop model hp. when i installed windows xp on it the graphics refuse to work and the second is sound. please help me.

anon85303
Post 22

I would like to know if a BIOS update is an operating system dependent or hardware dependent feature.

anon71612
Post 20

This helped me for engineering in school.

anon70897
Post 19

my name is codrin and i have a problem. If I try to play MK armaggedon and it says Cannot locate Bios, who can explain to me where and how i can find the bios? Please answer me.

anon68140
Post 18

how do i correct the lack of sound from my computer after installing windows 7 ultimate. when i installed the motherboard P5P800-VM disk, a message stated that it is not supported by the OS. how do I correct that?

anon60669
Post 17

To shuper30: Your CMOS battery (little 3 volt wafer battery usually built into the motherboard) is bad. When you unplug your computer there is no electricity keeping your BIOS alive.

For this reason when your computer does the POST it uses the default date. Since the true time is always past the default date, your computer knows you will experience a problem with your computer "real time clock" after it is booted up.

It is not a major problem if you just keep your computer plugged in all the time or set your clock every time you boot up.

If you click on the task bar after windows loads you can set the clock yourself without going into the setup.

anon57236
Post 16

BIOS is a specific kind of ROM.

anon53334
Post 15

I wanted to get information about BIOS, whether it is ROM or not? But this article did not discuss it.

anon52549
Post 14

My computer can't boot normally. it always displays a comment to change my on board battery, but I've already changed it with a new one. What seems to be the problem?

anon44687
Post 12

when i am trying to restart the notebook, BIOS is not coming out.

flyer07
Post 10

i see no one here can fix this hard drive. it's back to the store for a refund, or i guess that no one read this.

flyer07
Post 9

Trying to install a new hard 500gb, but all i see no matter how you partition it is one(1)drive this size 13,1702 using windows xp. Its called a bios drive..What is wrong here? I am ready to take it back and get my money back ..Computer says it is a 500gb drive in all the settings.

lewisdale
Post 7

when i boot up my pc it reads no hard drive detected. Do you have any idea how i can fix the problem?

anon24604
Post 6

why my computer takes more than 4 minutes to load the dos windows vista (cpu by MSI) Thanks

sarwan
Post 5

How will i insert raid driver while installing?

anon12012
Post 3

which of the following cannot be affected by a virus?

hard drive, floppy disk, traditional ROM chip, flash ROM .

shuper30
Post 2

When my computer is booting up after being turned on, this message appears on the screen:

"Invalid configuration information - please run SETUP program.

Performing automatic IDE configuration

Primary Master: Disk Drive

Secondary Master: CD-ROM Device

Secondary Slave: CD-ROM Device

Time of day not set - please run SETUP program"

What should I do to resolve this problem and not see this message every time I turn on my computer?

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