The BIOS Explained: Boot Order, Video Memory, Saving, Resets & Optimum Defaults
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bios explainedYour computer’s BIOS (basic input/output system) is the low-level software that starts when you boot your computer. It performs a POST (power-on self test), initializes your computer’s hardware, and passes control over to the boot loader on a connected device. The boot loader then boots your operating system – Windows, Linux, or whatever else you’re using. The BIOS has a setup screen, which is used to configure a variety of low-level system settings.

Note that you shouldn’t change settings in the BIOS unless you know what you’re doing. We’ll walk you through modifying some of the most commonly-used settings – like your boot order – but you could potentially change low-level CPU and memory settings that could make your computer unstable.

Accessing The BIOS

You’ll need to restart your computer to access your computer’s BIOS. Press the appropriate key at the start of the boot-up process – often when the manufacturer’s logo appears on screen – and you’ll be taken to the BIOS setup screen.

The key you need to press is often displayed on-screen at the start of the boot process. It’s usually the Delete key, although some computers may use other keys like F2, Escape, 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 or perform a Google search for your computer’s model name and “BIOS key.”

Note that newer computers that came with Windows 8 The Windows 8 Guide The Windows 8 Guide This Windows 8 guide outlines everything new about Windows 8, from the tablet-like start screen to the new "app" concept to the familiar desktop mode. Read More have UEFI firmware instead of the traditional BIOS. UEFI serves a similar purpose, although you’ll need to access your UEFI BIOS through Windows How to Access the BIOS on a Windows 8 Computer How to Access the BIOS on a Windows 8 Computer Windows 8 simplified access to the BIOS. You don't have to remember a key combination, you can just use the Windows 8 boot options menu. We'll show you how. Read More .

bios explained

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.

You’ll need to use the keyboard to navigate through your computer’s BIOS. You should see a list of the keys you need to use displayed on-screen.

Generally, you’ll use the left and right arrow keys to switch between settings screens (the names of each screen are generally displayed across the top), the up and down arrow keys to select an option on the current screen, and the Enter key to select an option or enter a sub-menu. To re-order a list, use 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 key.

bios explanation

Boot Order

One of the most commonly changed options in a computer’s BIOS is the boot order How to Change the Boot Order on Your PC (So You Can Boot From USB) 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 . 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’s hard drive, a Linux live CD Windows Users: Here Is Why You Need A Linux Live CD Windows Users: Here Is Why You Need A Linux Live CD Read More in your disc drive, and a hackintosh system How To Build Your Own Hackintosh How To Build Your Own Hackintosh This "How to Hackintosh" guide outlines what you need to do in order to build a power PC Hackintosh. This guide shows you the way. Read More installed on 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 a “boot order” because it controls the order in which boot devices are tried. For example, a typical computer might have its physical DVD drive higher in the boot order list than its hard drive. This means that the computer will attempt to boot off the DVD drive first, booting any inserted operating system installation discs or live CDs. If there are no bootable discs in the DVD drive, the computer would try the next option in the list, which would likely be its hard drive.

If you want to boot off another boot device – such as your DVD drive, USB drive, or a network boot location – you’ll need to 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 that, on some computers, USB drives may not appear in the list unless they’re connected when you enter the BIOS.

bios explanation

Video Memory

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 – 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 may be able to allocate additional memory to the video memory or reduce the amount of RAM used for video memory, reclaiming some of it for system tasks.

BIOS Password

You can generally set a password in your BIOS, often on the security screen. The password can be used to control access to the BIOS itself, preventing anyone from entering your BIOS and changing its settings. However, you can also set a password that people must have to boot the computer. This password prompt shows up right when the computer starts – if the person doesn’t know the password, they can’t even start your computer and access the Windows login screen. This feature is more powerful than a simple Windows password – it prevents people from booting other operating systems from removable media devices.

However, someone with physical access to your computer could reset the CMOS Why Does My Motherboard Have a Battery? Why Does My Motherboard Have a Battery? Whether you’re using a desktop computer or a laptop, your computer’s motherboard contains an integrated battery. Unlike a standard laptop battery, the motherboard’s battery doesn’t power your computer while you're using it. Quite the opposite,... Read More to clear this password, so this won’t protect you if your computer becomes stolen 5 Things You Can Do To Potentially Retrieve Your Stolen Laptop 5 Things You Can Do To Potentially Retrieve Your Stolen Laptop Laptop theft accounts for millions of dollars of losses per year in the US alone. These figures not only include the physical value of the device, but also the associated costs when company information and... Read More and a thief really wants to remove the password.

bios explanation

Save or Discard Changes

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

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

(These options may be named something slightly different, but they’re available on all BIOSes.)

You could also use the appropriate keyboard shortcut to quickly save and exit – the F10 key for this BIOS.

how bios works

Optimized 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.

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

bios explained

Other Options

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, increasing their CPU’s performance What Is Overclocking, And How It Can Help Your PC, Tablet, & Phone [MakeUseOf Explains] What Is Overclocking, And How It Can Help Your PC, Tablet, & Phone [MakeUseOf Explains] Provided that you have hardware from a manufacturer who understands those principles, you can do plenty to juice up your system, whether it be a computer, tablet, or smartphone. One of the best things you... Read More at the cost of additional heat, power usage, and possibly instability. (However, these settings are locked on some BIOSes.)

You shouldn’t change settings unless you know what you’re doing, but if you need to change a BIOS setting – such as the boot order – you should now know how to do it.

Do you have any other BIOS-related questions? Leave a comment!

Image Credit: Laptop computer via Shutterstock

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  1. 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

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

    Great,great!!! Really well expalined

  3. 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.

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

    Thanks for those basic explanations. Very useful for beginners!

  5. 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.

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

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

  7. 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.

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

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

  9. 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 :(

  10. 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....

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

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

  12. 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.

  13. 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