What Is BIOS (Basic Input Output System)?

Everything you need to know about BIOS

by
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Tim Fisher
General Manager, VP, Lifewire.com
Tim Fisher has 30+ years' professional technology support experience. He writes troubleshooting content and is the General Manager of Lifewire.
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Tim Fisher
Updated on February 26, 2020
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Michael Barton Heine Jr
Lifewire Tech Review Board Member
Michael Heine is a CompTIA-certified writer, editor, and Network Engineer with 25+ years' experience working in the television, defense, ISP, telecommunications, and education industries.
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Article reviewed on Apr 15, 2020
Michael Barton Heine Jr

BIOS, which stands for Basic Input Output System, is software stored on a small memory chip on the motherboard. It's BIOS that's responsible for the POST and therefore makes it the very first software to run when a computer is started.

The BIOS firmware is non-volatile, meaning that its settings are saved and recoverable even after power has been removed from the device.

BIOS is pronounced as by-oss and is sometimes referred to as the System BIOS, ROM BIOS, or PC BIOS. However, it's also incorrectly referred to as the Basic Integrated Operating System or Built-In Operating System.

What Is the BIOS Used For?

An illustration of someone in the BIOS of a computer
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BIOS instructs the computer on how to perform basic functions such as booting and keyboard control.

BIOS is also used to identify and configure the hardware in a computer such as the hard drive, floppy drive, optical drive, CPU, memory, and related equipment.

How to Access BIOS

The BIOS is accessed and configured through the BIOS Setup Utility. The BIOS Setup Utility is, for all practical purposes, the BIOS itself. All available options in BIOS are configurable through the BIOS Setup Utility.

Unlike an operating system like Windows, which is often downloaded or obtained on a disc and needs to be installed by the user or manufacturer, BIOS comes installed from the moment the machine is manufactured.

The BIOS Setup Utility is accessed in various ways depending on your computer or motherboard make and model.

BIOS Availability

All modern computer motherboards contain BIOS software.

BIOS access and configuration on PC systems are independent of any operating system because the BIOS is part of the motherboard hardware. It doesn't matter if a computer is running Windows 10, Windows 8, Windows 7, Windows Vista, Windows XP, Linux, Unix, or no operating system at all—BIOS functions outside of the operating system environment and is no way dependent upon it.

Popular BIOS Manufacturers

The following are some of the more popular BIOS vendors:

Award Software, General Software, and Microid Research were BIOS manufacturers acquired by Phoenix Technologies.

How to Use BIOS

BIOS supports several hardware configuration options that can be changed through the setup utility. Saving these changes and restarting the computer applies the changes to the BIOS and alters the way BIOS instructs the hardware to function.

Here are some common things you can do in most BIOS systems:

  • Change the Boot Order
  • Load BIOS Setup Defaults
  • Flash (Update) BIOS
  • Remove a BIOS Password
  • Create a BIOS Password
  • Change the Date and Time
  • Change Floppy Drive Settings
  • Change Hard Drive Settings
  • Change CD/DVD/BD Drive Settings
  • View Amount of Memory Installed
  • Change the Boot Up NumLock Status
  • Enable or Disable the Computer Logo
  • Enable or Disable the Quick Power On Self Test (POST)
  • Enable or Disable the CPU Internal Cache
  • Enable or Disable the Caching of BIOS
  • Change CPU Settings
  • Change Memory Settings
  • Change System Voltages
  • Enable or Disable RAID
  • Enable or Disable Onboard USB
  • Enable or Disable Onboard IEEE1394
  • Enable or Disable Onboard Audio
  • Enable or Disable Onboard Floppy Controller
  • Enable or Disable Onboard Serial/Parallel Ports
  • Enable or Disable ACPI
  • Change the ACPI Suspend Type
  • Change the Power Button Function
  • Change Power-on Settings
  • Change Which Display is Initialized First on Multi-Display Setups
  • Reset Extended System Configuration Data (ESCD)
  • Enable or Disable BIOS Control of System Resources
  • Change Fan Speed Settings
  • View CPU and System Temperatures
  • View Fan Speeds
  • View System Voltages

More Information on BIOS

Before updating BIOS, check what version is currently running on your computer.

When configuring updates, verify that you've downloaded the right file for your motherboard and that the computer not be shut down part way through or the update canceled abruptly. Interruptions could brick the motherboard and render the computer unusable, making it difficult to regain functionality.

One way to avoid this problem is to use what's called a "boot lock" section of the BIOS software which gets updated on its own apart from the rest so that if corruption ensues, a recovery process prevents damage.

BIOS might check if the full update has been applied by verifying that the checksum matches up with the intended value. If it doesn't, and the motherboard supports DualBIOS, that BIOS backup can be restored to overwrite the corrupted version.

The BIOS in some of the first IBM computers were not interactive like modern-day implementations but instead only served to display error messages or beeps codes. Any custom options were instead made by modifying physical switches and jumpers.

It wasn't until the 1990s that the BIOS Setup Utility (also known as the BIOS Configuration Utility, or BCU) became common practice.

However, nowadays, BIOS has slowly been being replaced by UEFI (Unified Extensible Firmware Interface) in newer computers, which offers benefits like a better user interface and a built-in, pre-OS platform for accessing the web.