Simple Questions: What is the BIOS & What Does It Do?

If you are a casual computer user, you may have heard about the BIOS, or BIOS failures or Dual - BIOS motherboards, but you may not understand very well what all these terms are. What is a BIOS except a weird-sounding acronym? What does it do and why is it important? If you read this article you will learn the answers to these questions and more.

What is the BIOS?

BIOS is a low level software, the first software to run when you power up the system. For a better understanding of what low level software means, you should know that the programs installed on your system, that you use daily, like your browser, media player, office suite are high level software because they interact with the operating system. The operating system is a mid level software because it interacts with hardware components through drivers and the BIOS. The BIOS is low level software because it directly controls the way hardware components work.

The BIOS provides a number of services that allow users and higher level software to configure the settings for a computer's hardware components and to get direct information from those components. For example both the user and the software installed on a computer can learn the rotation speed of the coolers that are found in the computer case or the temperature of several components, including but not limited to the processor or the video card.

The term BIOS is an acronym for Basic Input/Output System. You should think of it as the software that intermediates data transfers between the hardware components of a system and the user or the software installed on that system.

How Does the BIOS Work & How to Interact With It?

BIOS are generally very small programs, with a size of up to 16 MB. Modern BIOSes have a user interface, usually called Setup Utility, where the user can configure many hardware settings.

On laptops or tablets you will often encounter simplified BIOS versions, in which the user can only set the time and a couple of other things like the boot order.

On more advanced motherboards like those found on desktop computers, the BIOS provides many options, including ways to configure the CPU clock or its voltage, the shared memory between the CPU and the GPU, the RAM latency and so on.

Configuring an advanced BIOS may be dangerous if the user doesn't know what every setting does and sets the wrong values, because the components of the system have limitations in the way they can be set. For example, asking the processor to work at a very high frequency can make it overheat, throwing the computer into an endless restart loop. To make sure that you are safe, configure the BIOS settings only after consulting your system's manual and be sure you know the capabilities of the hardware components you are setting.

Another job the BIOS has to deal with is to store these configuration settings when the system is powered off. To do this, it has a small amount of volatile CMOS memory, that is powered by a battery like the one in the picture below. The term CMOS stands for Complementary Metal–Oxide–Semiconductor, representing the technological process used to make this memory chip.

When referring to computers, CMOS is the memory chip that holds the hardware settings of the computer. To learn more about this subject, please check this article on Wikipedia.

If the battery of the CMOS memory chip is dead and it can no longer provide energy, the BIOS will use the built-in default settings and not the custom settings you have set.

Computers & Devices Cannot Start Without the BIOS

The most important task the BIOS must handle is making the transition from a mechanical, hardware gesture, like touching the power button to a more abstract level, like showing your operating system logo on the screen. This means that, when you power-up your system, the BIOS is the first program to run. Its job is to start the coolers, check power levels, run some quick tests that evaluate the health of the system's hardware and then load drivers and start the boot process for the operating system. If there is any failure during this process, the BIOS displays a message informing you of what is wrong. In the screenshot below you can see and example of a possible error.

Before the BIOS was invented in 1975 by a computer scientist named Gary Arlen Kildall, the operating system was the first software to run when a computer started. That meant that the computer could only run the built-in operating system. Also, an operating system failure bricked the computer, because no other software could repair it, since it was not able to run before the operating system.

We can understand that using a BIOS provides a plus of flexibility, allowing users to install the operating system they want or to repair the current operating system if an error occurs.

What is the Dual-BIOS?

The BIOS is located on the motherboard and it is a small Read-Only memory chip. The software on that memory chip is created by the manufacturer of the motherboard and you can see what it looks like in the picture below.

If this memory chip fails, the BIOS cannot be loaded anymore, and the motherboard cannot be used. This is why motherboard manufacturers use a Dual-BIOS system on their modern motherboard. Dual-BIOS means that there are two chips for storing the BIOS: one for the main BIOS and one for a backup copy. If the main BIOS chip fails, you are asked to restart the computer and the backup BIOS chip is used to load the BIOS with the default settings.

What is UEFI & What Does it Have To Do with the BIOS?

UEFI stands for Unified Extensible Firmware Interface and you can look at it as a modern and more powerful BIOS. It has the same role as the traditional BIOS but it includes more features like cryptography or remote diagnostics and computer repair, even when there is no operating system installed. This type of BIOS was invented by Intel and it was first released in 2005.

UEFI became popular after the Windows 8 operating system was launched, because it was the first Microsoft operating system to provide native support for it.

Just like traditional BIOS, the UEFI is customized by the manufacturer of the motherboard you are using. On tablets and laptops, the UEFI BIOS will display few customization options. In the picture below you can see how it looks like on a Surface Pro 2 from Microsoft.

On desktop computers, the UEFI BIOS will display many customization options, more than those you can find on traditional BIOSes.

If you would like to learn how to access the UEFI BIOS on Windows 8.1 devices, we recommend that you read this article: How to Boot to the UEFI BIOS on any Windows 8.1 Tablet or Device.


As you can see from this article, the BIOS is a key component of any computer or device and knowing how to use it can provide more flexibility and some performance benefits. Knowledgeable users and IT professionals can use the BIOS to squeeze the maximum performance possible from their computers and devices. If you are not much of an expert that's fine. The default BIOS settings usually fit the needs of a casual user and your system will work fine even though you don't fiddle with the its settings.

I hope that you found this guide useful. If you have any questions or something that you would like to add, don't hesitate to use the comments form below.