Technology Explained

The BIOS Explained: Boot Order, Video Memory, Saving, Resets & Optimum Defaults

Christian Cawley Updated 19-12-2019

Older desktop and laptop computers feature hidden software called the BIOS. Making changes to this can improve how your computer works—or impede it from running properly.

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But what is the BIOS? How do you access it, and what changes can you make when you do? Here’s everything you need to know about your computer’s BIOS, explained.

What Is the BIOS?

The BIOS (basic input/output system) lives on a chip that can be replaced or upgraded. It is the low-level software that starts when you boot your computer. It performs a POST (power-on self-test), initializes your hardware, and passes control to the boot loader on a connected device. This then boots your operating system—Windows, Linux, or whatever else you’re using.

What is a BIOS?
Image Credit: Henrique Pinto/Flickr

All of this is automatic, but the BIOS also has a setup screen, which you can access. Used to configure a variety of low-level system settings, you can use it to manage things such as:

  • Boot order
  • Video memory
  • Overclocking
  • Virtualization
  • Power management
  • Wake-on-LAN
  • Fan management
  • And much more…

Note that you shouldn’t change settings in the BIOS unless you know what you’re doing. One wrong move and you could change low-level CPU and memory settings that could make your computer unstable.

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So, make sure you’re familiar with your computer’s BIOS before saving any changes. Keep reading to see our tips for modifying some of the most used settings.

NOTE: This guide is specifically about BIOS. However, since 2010 BIOS has been gradually replaced by UEFI. Check our guide to what UEFI is and how it makes your PC secure What Is UEFI And How Does It Keep You More Secure? If you've booted your PC recently you might have noticed the acronym "UEFI" instead of BIOS. But what is UEFI? Read More for details.

Accessing the BIOS

To access the BIOS, first restart your computer. Press the appropriate key at the start of the boot-up process to access the BIOS setup screen. The key you need to press should appear on-screen at the start of the boot process. Note that if no keyboard is attached to your PC, you cannot access the BIOS.

Accessing the BIOS should be straightforward
Image Credit: Ivan PC/Flickr

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This is usually the Delete key, although some computers may use other keys like F2, Esc(ape), F1, or F10. If you don’t know the key you need to press and it isn’t appearing on-screen, consult your computer’s manual. Alternatively, perform a Google search for your computer’s model name and “BIOS key.”

Stuck? We’ve covered all the options for accessing the BIOS How to Enter the BIOS on Windows 10 (And Older Versions) To get into the BIOS, you usually press a specific key at the right time. Here's how to enter the BIOS on Windows 10. Read More  on all versions of Windows.

Navigating the BIOS

Note that every computer’s BIOS is different. Your computer’s BIOS may look significantly different from the screenshots here, or it may look similar but have different options.

To navigate the BIOS, use the arrow keys on your keyboard. A list of any other keys you need to use usually appears on-screen. Typically, you’ll use:

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  • The left and right arrow keys to switch between settings screens
  • The up and down arrow keys to select an option on the current screen
  • Enter to select an option or enter a sub-menu
  • The + and—keys to move items up and down in the list

If this sounds a bit complicated, it’s not—you’ll mostly use the arrow keys and Enter.

3 Most Commonly Modified Settings in the BIOS

With access to the BIOS achieved, you’ll find settings you should ignore—as well as some that might need changing. The most common BIOS settings for modification are:

  1. Changing the boot order
  2. Adjusting available video memory
  3. Setting a BIOS password

Here’s how to do each of these.

1. Boot Order

One of the most changed options in a computer’s BIOS is the boot order.

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After the BIOS starts and initializes your hardware, it passes control to a boot loader that boots your operating system. The boot order determines which device the BIOS passes control over to.

For example, let’s say you have Windows installed on your computer and a Linux live CD Windows Users: Here Is Why You Need A Linux Live CD Read More in your disc drive. (Alternatively, a USB drive plugged into your computer.) When you boot your computer, which operating system starts? The answer is determined by your boot order.

It’s referred to as such because it controls the order in which boot devices are checked for an OS. For example, a typical computer might have the DVD drive higher in the boot order list than the HDD. This means that the computer will attempt to boot any inserted operating system installation discs or live CDs first.

If there are no bootable discs in the DVD drive, the computer would try the next option in the list. This would likely be its hard drive. You can boot your PC from:

  • Optical drive (CD, DVD, Blu-ray, etc)
  • USB drive (hard disk, thumb drive, or even a USB optical drive)
  • Network drive

If you want to boot off another boot device, simply move it up in the boot order list. You’ll generally find the boot order on a screen named Boot or something named similarly. Use the + and—keys to rearrange devices in the boot order list.

Note: on some computers, USB drives may not appear in the list unless they’re connected when you enter the BIOS.

For more details, see our guide to changing the boot order on your PC How to Change the Boot Order on Your PC (So You Can Boot From USB) Learn how to change the boot order of your computer. It's important for troubleshooting issues and tweaking settings, and it's a lot easier than you think. Read More .

2. Video Memory

Select the correct memory mode in your PC's BIOS
Image Credit: Jeff Keyzer/Flickr

Computers with onboard graphics hardware, such as Intel’s integrated graphics, may have a Video Memory setting. Onboard graphics hardware doesn’t have its own memory as dedicated graphics cards do. Instead, it takes over a portion of the computer’s RAM and uses it as its video memory.

On some computers, a Video Memory option may allow you to control how this memory is allocated. You might use this to allocate additional video memory or reduce it, reclaiming some of it for system tasks.

3. BIOS Password

While your operating system should have a login password you can further secure your computer with a BIOS password.

This can be set to control access to the BIOS; however, you can also set a boot password. With this enabled, no one can access the operating system or any attached media.

Be aware that this isn’t a perfect security feature. Anyone with physical access to your computer could reset the CMOS Why Does My Motherboard Have a Battery? Did you know there is a battery on your computer's motherboard? Here's what the CMOS motherboard battery does and why you need it. Read More to clear this password.

What Does Save Changes and Reset Do in the BIOS?

Changes you make to BIOS settings don’t take effect immediately. To save changes, locate the Save Changes and Reset option on the Save & Exit screen. This option saves your changes then resets your computer.

There’s also a Discard Changes and Exit option. This is for if you make a mistake or decide you don’t want to change your BIOS settings at all. Just use this option to exit the BIOS setup screen without saving your changes.

(These options may have slightly different names, but they’re available on all BIOSes.)

You could also use the appropriate keyboard shortcut to quickly save and exit. Often this is F10 but again, this may differ on your BIOS.

What Happens When You Load Setup Defaults?

Your BIOS also contains a Load Setup Defaults or Load Optimized Defaults option. This option resets your BIOS to its factory-default settings, loading default settings optimized for your hardware.

Repair mistakes in the BIOS by loading setup defaults
Image Credit: Paul Schultz/Flickr

This performs a complete BIOS reset, wiping any BIOS passwords in addition to resetting hardware settings and your boot order.

You probably won’t use this, but it can be useful for quickly changing the configuration after adding new hardware.

Other Less Commonly Modified Settings in the BIOS

The BIOS contains quite a few other settings and options.

For example, there’s a System Information screen that shows information about the hardware in your computer. Overclockers may be able to use CPU settings screen to tweak their CPU’s voltage and multiplier. This increases CPU performance The Beginner's Guide to CPU Overclocking Overclocking is an art, but it's not magic. Here we share how overclocking works, complete with a step-by-step guide to safely get a performance boost out of your CPU. Read More at the cost of additional heat, power usage, and possibly instability. (However, some BIOSes lock these settings.)

Meanwhile, if your PC has support for virtualization, you can enable Hyper-V or Intel Virtualization Technology (or however it is labeled) in the BIOS.

For the full selection settings you can modify in the BIOS, check your computer or motherboard’s manual.

Use the BIOS to Optimize Your PC’s Setup

By now you should be familiar enough with your computer’s BIOS to make some minor tweaks.

But it’s important to know that you shouldn’t change settings unless you know what you’re doing. Simple tweaks include adjusting boot order or video memory and if you get anything wrong, the setup defaults will help.

Remember to make your BIOS selections carefully. Getting the BIOS settings wrong can lead to problems. It’s one of several PC maintenance mistakes 8 PC Maintenance Mistakes That Kill Your Hardware Lifespan PC maintenance isn't rocket science, but you could be making a handful of mistakes that are actually harming your hardware. Read More you can make.

Image Credit: 72soul/Depositphotos

Related topics: BIOS, Computer Maintenance, Jargon, UEFI.

Affiliate Disclosure: By buying the products we recommend, you help keep the site alive. Read more.

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  1. Nikhil
    July 28, 2020 at 7:21 pm

    Will I be able to get back all my data and files if I have set to load setup default in bios.it was by a mistake.now I have lost my windows.does it mean I have lost my files and data too.

  2. Padraig
    December 3, 2016 at 12:34 pm

    Hi, i have a compaq 620 which has a admin lock on it and cannot access the start up screen on windows 7. If i do a BIOS factory reset default will this bring it back so i can access the computer i.e windows 7 etc. I am hesitant to do but i cannot get the admin rights as it is a second hand computer that was mothballed.

    I hope you can help?

    Many thanks

  3. Igor Rizvic
    March 7, 2013 at 5:06 pm

    Great,great!!! Really well expalined

  4. Victor Ong
    March 5, 2013 at 8:25 pm

    The BIOS shown here will be outdated in a few years. Everyone's switching to UEFI BIOS's already. I have one. They are much cleaner, easier to use, and they still provide tons upon tons of functionality -- actually more than the traditional BIOS.

    • dragonmouth
      March 7, 2013 at 4:58 pm

      The one function that Microsoft is interested in is that they can control access to the motherboards by allowing only Windows to run on them.

    • Meme
      October 31, 2016 at 8:13 pm

      If you cannot access or boot up your system in order to get to these shortcut, easy menus, then F2 is your friend and necessary.

  5. robert
    March 5, 2013 at 6:29 pm

    Thanks for those basic explanations. Very useful for beginners!

  6. Ron Lister
    March 5, 2013 at 3:26 pm

    If not sure about what your doing in bios probably shouldn't mess with the settings, but if you do make changes at least write down or record what each of your original settings are, before you make changes so they can be put back if necessary. Even if you do know what your doing, just takeing a picture of the original bios settings screens with your smart phone before making any changes can be a big help. I learned that lesson earlie.

  7. kunal
    March 5, 2013 at 3:08 pm

    A nice article giving simple and clear view of BIOS ...I like it ..

  8. Ian Hart
    March 5, 2013 at 12:46 pm

    I use the BIOS to swap between my two system drives, I have Ubuntu and Windows 8, saves messing around with boot loaders as each drive only sees each other as a bunch of files.
    Another great use is to control the speed of the CPU fan, mine used to roar like a jet taking off! slowed it down and set the temp perimeters to kick in if things get hot.

  9. Alexander Carstensen
    March 5, 2013 at 8:41 am

    Great guide ! Handy to know a few "tricks" that you can do via bios.

  10. Nevzat Akkaya
    March 5, 2013 at 6:54 am

    So many different BIOS'es out there, so many useful settings buried inside. Unfortunately manufacturers hide the most BIOS settings in laptops :(

  11. vineed gangadharan
    March 5, 2013 at 5:15 am

    neat article but you should have explained more functionalities

    • Adrian Rea
      March 5, 2013 at 6:45 am

      such as......?

      • Aditya Roy
        March 5, 2013 at 3:19 pm

        the only thing that comes to mind is updating BIOS

      • vineed gangadharan
        March 5, 2013 at 4:32 pm

        cmos's features ,,,i am confused with the options it has got....

  12. Partha Sarathy
    March 5, 2013 at 3:24 am

    Thank you..Now I have a better understanding of bios

  13. Kirby
    March 5, 2013 at 12:09 am

    "Use the + and – keys to rearrange devices in the boot order list." Some BIOS uses 'x' key to add / remove selections on the boot order list.

    You could also add to this article about flashing / updating BIOS although I don't think its really needed for new motherboards.

    • Adrian Rea
      March 5, 2013 at 6:45 am

      yep, well said. Also f5and f6, PageUp and PageDn or just Spacebar to cycle through options.
      I agree about discussing about updating the bios to the latest available version.
      Resetting the bios is a topic in itself, removing the battery, using jumps or even a reset bios cd.
      I access over 30 different bios a day and even the same make and model can have different bios to correct. The f10 action in HPs is a nightmare sometimes, with mis bios just changing the attributes and then save and exit is enough on most bios but with many HP you need to f10 each time you change a variable as well as a couple of f10 to save and exit.
      Changing the bios to PXE boot can be tricky. Some bios have the option, others bury it, needing you to enable the NIC, then on another menu allow to boot over LAN and then you sometimes need to reboot in order to see the PXE option in the boot order.

  14. Garris Rago
    March 4, 2013 at 11:34 pm

    I hope I'm not the only one who pretends I'm a computer genius when I do things in the bios as fast as possible :L haha