BIOS (Basic Input Output System)

BIOS, which stands for Basic Input Output System, is software stored on a small memory chip on the motherboard. You might need to access BIOS to change how the device works or to assist in troubleshooting a problem.

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.

Note: 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.

BIOS instructs the computer on how to perform a number of 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, etc.

The BIOS is accessed and configured through the BIOS Setup Utility. The BIOS Setup Utility is, for all reasonable purposes, the BIOS itself. All available options in BIOS are configurable via 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 is pre-installed when the computer is purchased.

The BIOS Setup Utility is accessed in various ways depending on your computer or motherboard make and model. See How to Access the BIOS Setup Utility for help.

All modern computer motherboards contain BIOS software.

BIOS access and configuration on PC systems is 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.

The following are some of the more popular BIOS vendors:

• Phoenix Technologies
• IBM
• Dell
• Gateway
• BYOSOFT
• American Megatrends (AMI)
• Insyde Software

Note: Award Software, General Software, and Microid Research were BIOS vendors that were acquired by Phoenix Technologies.

BIOS contains a number of 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
• 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

Before updating BIOS, it's important to know what version is currently running on your computer. There are multiple ways to do this, from checking in the Windows Registry to installing a third-party program that will display the BIOS version.

If you need help, see our How to Check the Current BIOS Version on Your Computer guide.

When configuring updates, it's extremely important that the computer not be shut down partway through or the update cancelled abruptly. This could brick the motherboard and render the computer unusable, making it difficult to regain functionality.

One way this is avoided is for BIOS to use what's called a "boot lock" section of its software that gets updated on its own apart from the rest so that if corruption is found, a recovery process can be undergone to prevent 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 BIOSes 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.