What is BIOS (Basic Input/Output System)?

BIOS, which stands for basic input/output system, is software stored on a small memory chip on the motherboard.

BIOS will be there to start and test your hardware and load your operating system from your hard drive whenever you boot up your computer.

In short, BIOS is what makes it possible for your operating system to communicate with all of the devices in your computer.

Why Do We Need BIOS?

We’ll explain the hardware-to-software relationship in this post for those who are less technically inclined.

When powering on a computer, it has to start somewhere.

Suppose you’ve ever restarted your phone when it freezes up or rebooted your router when your wireless internet connection is acting up. In that case, you’re familiar with the concept of a computer needing a fresh reboot every once in a while.

Since computers can’t press a button to restart themselves without human intervention (yet), they need another method for booting up again after being turned off.

This is where the BIOS comes in—it’s what allows all of that to start and stop.

To put it simply, BIOS initiates access to all the hardware components that make up the computer system at startup.

Hard Drive/SSD, CPU, RAM/memory modules, and graphics card and then checks that they’re working correctly together—this process is called POST (Power On Self Test).

When possible issues are flagged during POST by BIOS or an error is detected (e.g., dead battery), users will see an error message displayed on the screen, alerting them of the problem.

BIOS also acts as a security barrier between your operating system and any viruses that might try to infect it by preventing boot sector viruses from taking hold in the machine’s boot sector.

However, BIOS isn’t enough on its own to prevent viruses from infecting your device—you should also be using antivirus software for comprehensive protection against malware and other cyber threats.

Functions of BIOS

When you boot a computer, the BIOS does the following:

  1. The BIOS starts the computer by running software stored in ROM. This software is called firmware because it is permanently stored in hardware, which makes it different from other types of software that may be stored on a hard drive or CD-ROM.
  2. The BIOS looks for and configures hardware devices such as the keyboard, mouse, floppy drive, CD-ROM drive, hard drive, etc. Suppose a new device is added to the computer (an internal modem). In that case, you will need to run the BIOS Setup program to configure it.
  3. The BIOS finds and loads an operating system from a hard drive or CD-ROM. Suppose more than one operating system exists on your computer (Windows XP and Linux). You can use your computer’s setup program to select which one to load when starting your computer.

Difference Between BIOS and CMOS

CMOS is sometimes considered an alternative to BIOS, which is not the case. BOS is a type of firmware that has been around for several decades.

The original version of the Basic Input/Output System was coded using assembly language, which had to be hard-coded for each type of computer that ran it.

Today, most versions of the BIOS use CMOS memory to store the system configuration data, along with other settings such as boot sequences and system passwords.

The part where you enter your password at startup is the basic input and output area. You can also access your BIOS menu with key changes on your keyboard while your computer boots up.

How Do I Enter BIOS?

How to enter BIOS set up is different with each computer, but these are some common ways to enter BIOS:

  • F1
  • F2
  • Del/Delete
  • Esc

If your computer doesn’t boot normally, you may have to try to get it right a few times.

If you made it into BIOS setup and the welcome message doesn’t display on the screen, press a key on the keyboard or move the mouse.

If that doesn’t work:

  • Shut down and restart your computer.
  • Follow the steps above to reaccess the BIOS setup program.
  • Press a key or move your mouse if prompted by a message on your screen

How To Update BIOS

If you want to update your BIOS, check your motherboard’s manufacturer’s website for instructions.

  • You will likely need to download the latest BIOS from the manufacturer’s website. Be sure to back up all of your important files first!
  • Make a bootable USB key on another computer using the latest BIOS image you downloaded.
  • Insert this key into your computer and reboot, following any special instructions provided by your motherboard’s manufacturer.


So now you know what BIOS is, how it works, and can navigate the BIOS settings.

BIOS is a low-level system that’s been sidelined on most computers in favor of UEFI (Unified Extensible Firmware Interface), which offers additional features like mouse support, a graphical interface, and hard drive partitions greater than 2 TB — but you’ll still sometimes need to access and reconfigure BIOS for basic tasks.