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The PC BIOS: The 'Basic Input Output System' Setup Program and UEFI/EFI Used in Desktop and Laptop Computers/PCs - Page 1

This section of this website should provide the owners of desktop and laptop PCs with all of the information they need to know about the old-style standard legacy BIOS setup program that starts up from battery-powered flash RAM memory and the new UEFI BIOS that starts up from permanent, non-volatile memory that doesn't use the motherboard's battery when the computer is turned on, which then configures a computer’s hardware so that the operating system, mostly Windows, can recognise it and load its software device drivers. A standard legacy BIOS can be entered to examine or change its settings before Windows starts to load by pressing its entry key, which is usually the Del or F1 key. An instruction on the startup screen says something like: “To enter setup press Del” or “DEL: Setup”.

Most Windows 8.0/8.1 and Windows 10 PCs use a UEFI BIOS (instead of a standard legacy BIOS) that can be set in UEFI or standard legacy BIOS mode. Here is information on how to do that if the UEFI makes it possible in the first place:

Note that if you are using a wireless keyboard, it might not allow you to enter the BIOS. In which case, you’ll have to use a wired PS/2 or USB keyboard. Moreover, when a desktop or laptop computer starts up – boots – only certain USB ports might be active during the boot, so, if you are using a wired USB keyboard and you can’t access the BIOS, try using the other USB ports.

Common BIOS-related problems are dealt with here instead of having their own section, because there aren't many of them. Information is provided on the new UEFI BIOS, also know as an EFI BIOS, which is required for hard disk drives that have a storage capacity greater than 2.19GB.

I have dropped the U and called it the EFI BIOS on this page just because it is shorter.

Note that the settings that are made accessible in a BIOS depend on the computer's manufacturer or the motherboard's manufacturer if you buy or build a PC and install your own motherboard. If the computer is made for gaming enthusiasts, for example, if will no doubt provide a full range of customisable BIOS settings, such as settings that allow the overclocking of the components, running them faster than their stock speed, whereas if it is made for the typical home user, the computer manufacturer will probably provide only the basic settings in order to prevent the user from messing about in the BIOS and causing problems that require solving from its expensive support staff. For that reason, most laptop and netbook computers usually don't have a BIOS that allows much in the way of customisation.

There is too much information to provide a contents menu. Instead, the information is presented to make it easy to see what is dealt with by scrolling down the two pages of this article. I prefer having long Wikipedia-style articles that can be scrolled to having the information spread over ten or more short pages.

Introduction to the BIOS setup program

Visit Page 2 of this article if you are only looking for information on reflashing the BIOS to update it.

Updating an EFI BIOS used on motherboards manufactured by the major manufacturers is usually just a simple matter involving nothing more than downloading the update, transferring it to a flash drive, plugging the flash drive into a USB port and pressing a button on the motherboard, as shown in the following video. The method might differ from manufacturer to manufacturer, but it will always be simple.

ASUS How-To - Install CPU, CPU Fan, & Memory -

Shows how a UEFI BIOS is updated by installing a USB flash drive containing the update and pressing a button on the motherboard. When the light on the button flashes the UEFI is updated.

Note that if you are looking for information on reflashing the BIOS of a tablet PC, some of them have a standard PC-type BIOS that can be accessed and reflashed and others use inaccessible firmware that can only be updated. The tablet manufacturer's website should provide information un how to perform a reflashing. If not, some manufacturers provide email and forum support. Also, Amazon runs forum topics on some products that are accessed from the product's buying page, such as the following thread that provides advice on how to update the firmware of a popular 7" tablet PC:

The BIOS setup program - an acronym for Basic Input/Output System - is a vital part of a PC's system, without which nothing can work. It was present in the first PCs made by IBM and is still in use in 2012, more than 30 years later. The standard keyboard-driven BIOS configures the PC's hardware so that the operating system (Windows, Linux, OS X, etc.) can recognise all of it and install the appropriate software device drivers. The program itself is stored in a CMOS flash memory chip on the motherboard and it can be upgraded by reflashing the memory chip with the update according to predetermined procedures. However, it is being replaced by a mouse-driven Unified Extensible Firmware Interface (UEFI) BIOS, also known simply as an EFI BIOS, which is what I will be calling it in this article.

Motherboard battery

Note that desktop and laptop PCs now store the EFI settings in non-volatile permanent memory that retains information when the PC is switched off, which means that the EFI does not require to make use of a battery supplied by the PC's motherboard to retain its data. However, motherboards still have a battery because the Real Time Clock (RTC) that keeps date and time information has to be powered. The operating system takes its date and time from the RTC. The EFI is not accessed by pressing an entry key (Del, F1, etc.) at startup, it is accessed from within Windows 8.1 and higher versions of Windows. The following video shows the easiest but still very involved way in which to get into the boot menu in Windows 8.1 in order to access the EFI settings.

Windows 8.1 - Accessing the UEFI (BIOS) Setup -

Changing the boot order of devices in a UEFI BIOS to enable booting from USB flash drives and CD/DVD drives

The video linked to below deals with changing the boot order of devices on a new laptop which has a UEFI BIOS. The man wanted to boot from a DVD disc created using his backup software, but if you want to boot from a USB flash or USB external drive, you set the boot device to the USB setting. He disabled the UEFI's Secure Boot, which does not allow the system to boot from unknown media or devices, and changed the UEFI BIOS to a standard BIOS by choosing the CSM Boot. The man set the first boot device to his laptop's DVD drive. The other boot-device options shown in the video are HDD/SSD  - hard disk drive or solid state drive, which will boot the operating system (Windows 8.1 and 10 that use an UEFI BIOS. Windows 7 and earlier versions do not use a UEFI BIOS - USB, the  setting you want to set as the first boot device to boot from a flash drive, and LAN, which is booting from a home Local Area Network.

How to Fix Issue Booting to DVD/CD with New UEFI BIOS Boot Order -

How to recover a Windows PC from boot problems introduced by the replacement for the standard BIOS called the UEFI BIOS

If your new computer running Windows 8.0/8.1 or Windows 10 won't boot from a backup-rescue disc or some other boot disc, the Secure Boot used by the new UEFI BIOS is usually the cause of the problem.

Windows PCs started using the UEFI BIOS, which is the replacement for the decades-old standard BIOS, with the release of Windows Vista in 2005, so most desktop and laptop PCs bought new since then use a UEFI BIOS.

The standard BIOS, stored in a flash-RAM chip, boots before Windows to run the Power On Self Test (POST) that checks that the hardware components are functioning and configures those components for Windows so that it can load their software device drivers. The standard BIOS of a PC can provide many configuration settings, depending on how many the desktop or laptop PC manufacturer is prepared to allow. The manufacturers of laptop and desktop PCs used for office work usually prefer to have the BIOS or UEFI as limited (or difficult to access, as in the case of the UEFI BIOS) as possible in order to prevent users from getting into the kind of trouble that requires costly customer support. However, PCs or motherboards or laptops bought by power users usually have a BIOS or UEFI that provides the customisation settings that such users are likely to want or need, such as those that allow the processor and RAM memory to be run at higher frequencies than their stock frequencies (to be overclocked), either by enabling settings manually or enabling automatic settings.

The early versions of the UEFI BIOS used in PCs running Windows Vista were more or less the same as the standard BIOS but with mouse operation instead of keyboard-only operation of a standard BIOS. All devices require a device driver to operate, so the keyboard and mouse drivers have to be loaded by the BIOS/UEFI itself in order to be used. The flash-RAM chips of the standard BIOS were of small capacity due to the cost of flash-RAM, so only keyboard navigation was used.

Windows 7 PCs came with a more developed UEFI BIOS that allowed access to the settings while running Windows.

If you are still using Windows 8.0, you should upgrade to version 8.1 in order to be able to get patches and security updates, because Microsoft only supports Win 8.1.

Windows 8.1 and Windows 10 make as much use of its UEFI as the manufacture is prepared to provide, such as providing startup protection from rootkit infections. Rootkit infections operate under Windows, so require special software to detect and remove them that can be updated like anti-malware scanners.

Unfortunately, UEFI protection is intrinsically bound to the installation of Windows 8.0/8.1, thereby making it problematic to boot the system with another operating system's boot disc (for example, Ubuntu Linux can be run from its boot disc or be installed on the system) or to run system-boot recovery/repair discs created by third-party developers. The UEFI protection itself prevents that from happening unless special measures are adopted.

The following link goes to an excellent article that explains and illustrates how to overcome those UEFI boot problems.

How to solve UEFI boot and startup problems -

Shutting Windows 8 down completely in order to be able to enter the BIOS

Note well that Windows 8 never shuts down completely, it goes into a deep sleep mode similar to hibernation, starting up from where it left off.

By default, Windows 8 never shuts down all the way due to a new feature — fast startup, which is dealt with in the following article.

Delivering fast boot times in Windows 8 -

An EFI BIOS can behave as a standard BIOS for operating systems that require one, but provides additional functions for an operating system that supports an EFI BIOS, such as Windows 8. A windows 8 computer with an EFI BIOS can boot very quickly indeed, especially with a solid-state boot drive (SSD). The following video shows a laptop booting fully in a few seconds.

Microsoft demos fast boot times in Windows 8

However, note well that, as with the hibernation mode used by XP, Vista and Win7, you won't be able boot into the BIOS from the default shutdown by pressing its entry key (Del, F2, etc.). A full shutdown is required because the BIOS isn't accessed during a fast startup, just as it isn't when it comes out of hibernation.

Some computer manufacturers provide a way of shutting down completely. For example, Acer’s shutdown icon allows the user to select Sleep, Hibernate, Restart or Shutdown. To shut down all the way, the Shift key is held down while the shutdown icon is clicked. The Shift is held down until the machine powers off completely. You must find out from its user manual if a new Windows 8 computer provides a similar option.

Fast startup can be disabled via the Shutdown settings in Power Options. On the desktop screen, open the Control Panel, click Hardware and Sound/Power Options/System Settings. At the bottom of the dialog box you can disable Turn on fast startup. Now you will be able to enter the BIOS at startup by pressing its entry key.

An EFI BIOS can do far more than a standard BIOS, such as providing overclocking, and the mouse/laptop touchpad can be used to access and navigate through its sections, it runs much faster than a traditional BIOS and can even access the web. It is in fact a mini operating system that kicks in at startup to prepare the way for the main operating system.

Secure Boot operates from an EFI BIOS that is the program that a computer uses to boot the system. It protects the system by guarding against unauthorised operating systems and pre-boot attacks. Windows 8 supports Secure Boot. Any other operating system, such as a distribution of Linux, that does not support it, won't be able to boot the system. A switch inside the EFI BIOS, forces it to validate the boot code against digital certificates within the EFI. No validation, no boot. Note that if the computer uses a standard BIOS, not an EFI BIOS, Secure Boot cannot be supported. Therefore, if you've been using a Linux boot disc, such as Ubuntu Linux, with an earlier version of Windows and it fails to boot the system using Win8, you know what the problem probably is. Try updating the boot disc. The following Q&A on this website discusses the EFI and Secure Boot.

EFI BIOS, Legacy BIOS, Windows 8, Secure Boot and Linux and dual boot Windows 7/Windows 8 problems and questions -

Because an EFI BIOS can’t perform the POST (Power On Self Test) that checks that all of the computer's devices are present and working or run the initial setup - configuring the memory, hard drive(s), processor and other hardware - many computers use both a standard BIOS and an EFI BIOS. The standard BIOS runs first to do what the EFI can't do and then hands over to it. Computers that have the EFI but no standard BIOS have separate programs that run the POST tests and setup automatically at system startup.

With further regard to an EFI BIOS and Windows 8, if you don't have a COA/Product Key sticker on the computer but you have the Windows 8 installation disc this indicates that the system has an EFI. The certificate is recorded in ROM chip on the motherboard. The OEM Win8 installation disc has an XML file in the installation routine that calls the Product Key from ROM chip during installation, so it is not provided on the machine itself. The system documentation is also probably provided somewhere on the hard disk drive.

If both EFI and Legacy (standard BIOS) are enabled in the BIOS, the system is almost certainly EFI/GPT (uses a GPT file system) and Legacy is enabled to allow booting the system from CD/DVD disc that is not EFI-aware. If the OEM setup is EFI and you were to disable EFI, Windows won't boot. Note well that all new OEM (brand-name) Windows 8 PC's/laptops use an EFI.

GUID Partition Table [GPT] -

Note that the PC's motherboard must have an EFI BIOS in order to use a hard disk drive with a capacity higher than 2.19TB (2190GB, using 1000MB = 1GB and 1000GB = 1TB used by hard-drive manufacturers, not the 1024MB = 1GB, 1024GB = 1TB system used by software developers).

The motherboard manufacturer, Gigabyte, has taken this a step further with its Touch BIOS, an EFI BIOS that can be accessed by touch when using a touch-sensitive screen that desktop monitors and laptop PCs are beginning to have. The keyboard had to be used to navigate a standard BIOS. An EFI BIOS is accessed at startup in the same way as a standard BIOS - by pressing a key (Del, F1, etc.) provided on the first boot screen in a message that reads something like: Press the Del key to enter Setup.

A particular make/model of motherboard's user manual has a section devoted to the BIOS that describes the features and settings. The manual comes with a new motherboard or can be downloaded (usually in the PDF format) from the manufacturer's website by searching for that model of motherboard's support page.

The image below is of an EFI BIOS used by an MSI motherboard that was current in May 2011, which also provides overclocking, games and utilities. The main settings are accessed by clicking on the Settings icon. Navigation can be done with keyboard arrow keys or by using a mouse/laptop touchpad. The user interface is far more graphical than the basic interface of a standard BIOS, images of which are shown further down on this page. The indication that it is an EFI BIOS are the words in its title - Efficient. Flexible. Intelligent.

MSI motherboard MS7673 EFI BIOS main menu  page

Here is a video that shows how to use the the 2D and 3D EFI BIOS of a Gigabyte motherboard and overclock the Intel i5 3570K processor:

Gigabyte Z77X-UD3H Ivy Bridge i5 3570K Overclocking Tutorial + EFI Demo

The 3D EFI BIOS provides a 3D model of the motherboard. By just placing the mouse over a component provides the information that the BIOS provides on that component. For example, by placing the mouse over the processor provides its current clock speed, the motherboard's base clock speed that the processor multiplies to obtain its own clock speed, etc. Where the base clock speed is, say, 100MHz and the clock multiplier is set at 24x in the BIOS, the processor's running clock speed is 2,400MHz, which is 2.4GHz. With a multi-core processor, each core will be running at that speed.

There are several other overclocking-related videos provided on that page.

Note that a hard disk drive with a capacity higher than 2.19GB requires a computer with a motherboard that provides an EFI BIOS and runs a 64-bit (not a 32-bit) operating system. Read the following Q&A on this website for more information on this topic: Can an ultra-large-capacity 3.0TB hard disk drive be used with Windows XP, Vista or Windows 7?

The following thread from a computer forum on the EFI BIOS is well worth reading:

Adventures with UEFI -


Motherboard battery

Note that desktop and laptop PCs now store the EFI settings in non-volatile permanent memory that retains information when the PC is switched off, which means that the EFI does not require to make use of a battery supplied by the PC's motherboard to retain its data. However, motherboards still have a battery because the Real Time Clock (RTC) that keeps date and time information has to be powered. The operating system takes its date and time from the RTC. The EFI is not accessed by pressing an entry key (Del, F1, etc.) at startup, it is accessed from within Windows 8.1 and higher versions of Windows.

Customised settings are maintained by having the chip powered by a legacy CMOS/BIOS battery on the motherboard, shown below (made by Sony), which should last five or more years. You can buy very cheap replacement batteries from all good retail and online computer shops. You must buy the correct type. The battery shown in the image below is a CR2032 non-rechargeable coin battery. You must never use a non-rechargeable battery if a rechargeable one is required (as is the case with a wireless phone that recharges its battery), because it can explode. Using CR2032 in a web search provides links to online sellers.

Close-up view of a Sony BIOS battery and the BIOS chip on a motherboard

If the battery runs down, the system reverts to using the default BIOS settings every time the PC boots, which is fine, since most users don't customise their PC's BIOS settings by choosing non-default settings in any case and most PCs operate perfectly well using the default settings.

If the BIOS battery runs down and Windows is not set under Date and Time in the Control Panel to synchronise with an Internet time server, you'll have remember to reset the date and time in Windows every time you switch the computer on. If the time and date is incorrect, the worst that can happen is that Windows will give newly-created files the wrong time and date.

Note well that it is a simple matter to replace the battery on a desktop PC's motherboard, but it can be extremely difficult to do so on most laptop PCs, because the motherboard is inaccessible without taking the laptop apart. Sending it to the manufacturer or taking it to a laptop repair shop to have a new battery fitted will be very expensive. Fortunately, the laptop will run perfectly well on the default BIOS settings that will be used every time the laptop starts up, but the real-time clock will have to be reset in the BIOS if both the mains power and the battery are disconnected. If the laptop is left charged or connected to the mains, the clock shouldn't require resetting.

For the battery installation the desktop or laptop PC's motherboard, there are three types of battery socket types. The following webpage show you how to replace all three types. -

The flashing utility used to reflash a BIOS CMOS chip with and update can be used to save the current state of the BIOS as a file to a floppy disk if the computer has a floppy disk drive, which most desktop and laptop PCs do not have now. Note that USB floppy disk drives are available, but the device driver have to be installed in order to be able to use one, which is not the case when the BIOS is opened at startup (before Windows can load the driver).

Alternatively, you can take digital photographs of the BIOS screens or press the PrtSc (printscreen) key to print each of the BIOS setup screens showing any customised settings. The current screen's display is sent to the printer port. Note that a parallel printer, not a USB printer or network printer, must be attached to the computer's parallel port (not via a USB adapter to a USB port), because the BIOS can only print to a parallel port. The item called BIOS tip: Saving or backing up the BIOS settings in the first table further down this page provides more information on this topic.

For how much longer the BIOS setup program will be used for start-up configuration purposes remains to be seen, because in Apple Macs the operating system, OS X, performs that function, and some of the leading players in the PC market, namely Microsoft and Intel are working together on a replacement for the BIOS called the Unified Extensible Firmware Interface (EFI), which is a mini operating system that supports a high-resolution full-colour graphical interface that allows various tasks to be run before the main operating system boots, such as basic multimedia operations, scanning for viruses, and the use of diagnostic tools. In any case, even with the existing PC BIOS, the operating system (Windows 7, Linux, etc.) has assumed many of the functions that used to be be performed by the BIOS.

The Unified Extensible Firmware Interface (EFI) will be used in new desktop and laptop PCs by 2011, making for much faster startup times and less hardware compatibility issues with new hardware components.

The BIOS setup program performs four distinct tasks:

1. - Tests the computer's main components by running its POST (Power-On-Self-Test) program to make sure that they are all functioning properly.

2. - Configures the main components that are part of the motherboard or that are attached to it so that the operating system knows what to do with them. The configuration role was essential to the operation of a computer, but it is decreasing all the time as the operating system continues to take over more and more of this role.

3. - Boots the operating system from the primary hard disk drive or from a bootable floppy disk or a CD/DVD disc at start-up.

Note that the floppy disk drive or CD/DVD drive has to be set as the first boot device in the BIOS in order to make the system boot from a floppy disk or CD/DVD. The settings for this vary from one make of BIOS to another, but you should be able to locate the appropriate setting by going through the BIOS menu. (Information on how to enter the BIOS is provided further down this page.) For example, in a Phoenix Award BIOS, in the Advanced BIOS Features section, you might see settings for First Boot Device, Second Boot Device, Third Boot Device, etc. You will be able to set a floppy disk drive, CD/DVD, or hard disk drive, etc., as the first boot device. Some BIOSes allow you to set a USB flash drive or external hard disk drive as the first boot device. If the first boot device contains no boot files, the BIOS uses the next boot device until it finds one that it can boot from.

For example if the CD/DVD drive is set as the first boot device and there is no boot CD/DVD disc in the drive, the BIOS will try to boot from the second boot device. The image below shows how the settings appear in a particular BIOS.

The page in an AMI BIOS setup program showing the settings for the boot order of devices - Floppy drive, USB drive, SATA hard disk drive

Note that the image above shows a BIOS menu screen that was used in 2005. The user interface provided by most current BIOSes has become easier to use since then, with the main menu also providing more features, such as overclocking settings in addition to the usual settings.

The following video shows how to use the Windows 7 installation DVD disc to boot the system and then access System Restore from the repair options that are provided. You are shown how to set the CD/DVD drive as the first boot device in the BIOS. Note that you can leave the BIOS set to boot from the CD/DVD drive first because if Windows doesn't detect a disc in the drive it boots from the next device set in the boot order of devices, which is usually the hard disk drive or SSD drive. Windows 7 can create a Repair Disc that can be used if you don't have an installation DVD. From within Win7, just enter Create system repair disc in the Start => Search programs and files box to be provided with a wizard that creates and burns the disc. -

4. - Provides access to some of the computer's components and features, such as the keyboard even when the operating system is up and running. The BIOS is programmed to run a small routine that handles the keyboard at the behest of the operating system. In this way, the BIOS code provides a uniform interface to the system in order that variable hardware can function without having to make the necessary changes to the operating system when the type of hardware changes. Windows 2000, Windows XP, Windows Vista and Windows 7 only make a small number of such calls to the BIOS, but the Linux operating system makes no such calls while it is running, because it deals directly with the standard hardware it is likely to encounter, and it uses device-driver software to deal with any non-standard or special hardware it encounters. Moreover, work is under way to create a version of Linux that boots without a BIOS.

5. - Reflashing. - The BIOS can be updated to remove bugs or support additional hardware by reflashing it with an updated BIOS file. The major motherboard manufacturers update the BIOS for their motherboards regularly. An good example in which installing an update is necessary is when a Socket 939 motherboard that runs AMD's Athlon 64 processors has a BIOS that supports only the single-core version of those processors. If the user wants to use a dual-core Socket 939 model, which the motherboard supports, a BIOS update is required. [Note that AMD-processor-based Socket 939 motherboards are no longer being sold new. Socket AM3 and Socket FM1 are AMD's current processor sockets for desktop PCs.]

The PC's motherboard manufacturer should be the only source that you should use to find BIOS updates and instructions on how to install them. The standard startup screen (shown in images lower down in this article) and the startup screen showing the logo of the computer's manufacturer should provide the instruction on how to enter the BIOS or Setup. Most manufacturers use the Del key, which is pressed before Windows starts to load to bring up the BIOS setup program. Dell uses the F1 key. The version of the BIOS is shown on the standard startup screen or within the BIOS setup program itself. If you cannot locate a higher version number that the existing version, an update is not available.

Visit Page 2 of this article for more information on reflashing the BIOS to update it.

Features can be added by programming them into the BIOS code. For instance, many laptop computers have special function keys that are not found on standard desktop computer keyboards, which have nothing to do with the operating system and control the screen's brightness, contrast, the volume of the sound, etc.

The PnP/PCI Configurations page of an Award BIOS setup program

The PnP/PCI Configurations page of an Phoenix Award BIOS is shown above. (PnP stands for Plug and Play.)

The PnP/PCI Configurations, shown above, and other pages in the BIOS, are reached from the main menu page, examples of which are shown further down this page. The settings are either enabled, often with parameters, or disabled. The browse menu appears on the bottom of the page. The keyboard has to be used because the mouse driver hasn't been loaded when the user enters the BIOS setup program, because neither DOS, (which starts up first in Windows 95/98/Me, but is absent in Windows XP) or Windows has loaded.

The Item Help section of each page provides information on the setting that is selected.

You shouldn't attempt to change the BIOS settings unless you know what you're doing, because the wrong settings can prevent the system from booting. But if that happens after you've changed settings, you can always enter the BIOS at start-up and change the settings back to what they were, or set one of the default options that have names such as, Load Fail-Safe Defaults and Load Optimised Defaults, both of which should remove any settings the user has enabled or disabled, and enable the system to boot.

Any customised settings in the BIOS are retained when the PC is switched off because a CMOS battery keeps the CMOS chip that contains the data powered up. The image below shows a Sony CR2032 CMOS battery installed in a socket on an ATX motherboard.

Close-up view of a Sony BIOS battery and the BIOS chip on a motherboard

The beep codes that provide information on errors

The BIOS can provide error-alert messages to the user of the computer by using sounds (usually one or more long or short beeps provided by the speaker built into the computer's case), text messages, or now even by issuing voice messages.

Obviously if the computer's video card doesn't work for some reason, a text error message is of no use, so most BIOSes issue a beep code to alert the user to an error in configuring the video card.

Should you need it, entering the search phrase bios beep codes in a search engine should produce many links to sites with beep-code information. If you know the make of the BIOS - e.g. - Award or AMI - use the make in front of the search query, such as: award bios beep codes.

Note that the PC must have a speaker built into the case, which laptops always have but which not many PC have now, in order to be able to hear the beeps. Read the PC's user manual to find out how the BIOS reports error messages. Some motherboards use codes displayed on an LED display on the motherboard or on a display at the back of the case that you have to look up. The information is usually provided in the motherboard's user manual and/or online. Most motherboard manufacturers provide user manuals for their boards in the PDF format online.

A talking BIOS

Some motherboards are now offering a talking BIOS, which speaks its error messages. Obviously this will only be of any benefit if the sound system it uses is working. Since the sound card is not available until DOS (with DOS sound card drivers loaded) or Windows have started up, it would have to make use of the small speaker built into the computer's case that issues the start-up beep, and other BIOS beep codes.

To name one, the Supermicro 845G P4SGA motherboard is fitted with a talking BIOS.

Intel Extreme Memory Profiles (XMP)

A computer with a specific Intel Core i5 and i7 processor (first and second generation) should have a BIOS that supports Intel Extreme Memory Profiles (XMP). Most but not all RAM memory kits can make use of this technology, which replaces the plethora of memory settings with a single setting that just has to be enabled in order to function automatically with the optimal memory settings.

DDR3 Overclocking with Intel® Extreme Memory Profile -

How To Enable XMP Performance Profiles -

BIOS tip: Saving or backing up the BIOS settings

If you have spent a lot of time to customise the BIOS settings for your PC or you want to experiment to find out what the best settings are, you can use a digital camera to take photos of every page in the BIOS so that you can refer to them if you want to revert to a particular range of settings. You have to do that to record what is on the pages because the print screen (operated via the Prt Sc key) option doesn't function until the operating system is loaded, so you can't transfer a captured image to a Windows program.

When printers were primitive and had to have their own processing unit in order to work, it was possible to use the Prt Sc key to make the printer print what was on the PC's screen. If you are using a non-USB printer - one that uses the old (legacy) Centronics or LPT1 parallel port interface) - that option could work. However, with USB printers, which most users now have, you cannot do that.

If your PC has a floppy disk drive, which most new PCs no longer have, the following article provides information on how to back up the BIOS settings to a floppy disk.

BIOS Backup -

You can find other such articles by using the web search term bios backup to find many articles on how to do it.

You can save a file containing your BIOS backup on a recordable CD/DVD. You need to make the disc bootable and and know how to make your computer boot from a CD/DVD in order to be able to make use of the backup. Use the web search term create a bootable cd to find many articles on how to do it.

The BIOS has to be set so that the first boot device is the CD/DVD drive in order for the system to be able to boot from a CD/DVD disc. Just open the BIOS and look for the boot order settings.

The Reset Configuration Data BIOS setting

Resetting the BIOS itself (dealt with further along in this article) so that the entire BIOS is reset must not be confused with its Reset Configuration Data setting (shown in the second image from the top of the page) that resets its hardware configurations. That setting is enabled and the BIOS resets what the BIOS knows about all of the hardware components and peripheral devices (printers, etc.) and then disables the option so that its isn't repeated with every system startup. All of the existing hardware configuration data is erased and then replaced, giving a fresh start that can resolve many hardware misconfiguration problems.

The following problem is the type of problem that can be resolved by using the Reset Configuration Data setting in the BIOS: "I was changing the screen resolution on an older Intel Pentium III computer running Windows XP Pro when the screen went blank and said, 'not supported, 87Hz.' Only the first boot screen appears, which allows me to enter the BIOS, otherwise the screen remains blank."

A CR2032 CMOS battery is not designed to be rechargeable; that is, to be able to go from being fully charged to being fully discharged and then recharged repeatedly. However, it does receive a trickle charge when the computer is switched on. This extends the life of the battery considerably if the computer is used regularly. Such a battery can last up to five years or more. However, it discharges completely in a few weeks if the computer isn't used, because it keeps the CMOS BIOS chip powered up. The motherboards are shipped from China with the CMOS jumper it its disconnected position to prevent the battery from discharging.

Most motherboard vendors and PC manufacturer's set the jumper in its enabled position when the motherboard or PC containing the motherboard is sold. However, motherboards can be sold with the jumper in its disabled position, which renders the PC that uses a motherboard in that state unable to retain customised settings. A dead or disabled CMOS battery usually produces an invalid-settings or settings-lost message at startup, not a blank screen. The user would then have to enter the BIOS and enable and save its default or failsafe or optimal setting every time the PC starts up.

With ATX motherboards, the power supply provides power to the CMOS chip if the PC itself is switched off but is attached to the mains supply, which is switched on. A user who unplugs the PC from the mains or switches the power off at the mains supply, will shorten the life of the CMOS battery.

This Q&A on this site deals with the problem that its title describes: Why is my computer running slow after I replaced a flat BIOS battery on the motherboard?

The startup screen for a system running an American Megatrends (AMI) BIOS and an AMD Athlon 64 3200+ processor is shown below.

Note that if you see the logo of the motherboard's manufacturer or the developer of the BIOS instead of such a startup screen, you should be able to disable the logo in the BIOS itself. The standard startup screen of the kind shown below will then display. Click here! to go to more information (on the next page of this article) on disabling a logo startup screen. Some BIOS setup programs allow the logo to be temporarily disabled so that you can see the startup information by, for example, pressing the Tab or Esc key during startup.

The figure in Checking NVRAM... 1048576KB OK is 1GB of RAM that was found to be present and checked during the POST (Power-On-Self-Test) set of hardware tests that all computers initiate on starting up.

The start-up screen for a system running an AMD Athlon 64 3200+ processor

DRAM Clock = 400MHz: The system's DRAM clock is shown as 400MHz, so DDR400 (PC3200) RAM) is installed.

DEL: Setup: Pressing the DEL key enters the BIOS setup program.

The different brand-name computer manufacturers and BIOS setup program developers use different keys or key-combinations to enter the BIOS. Visit this page if you need to know what the entry methods used by all of the main brands of PC and the major BIOS developers are:

Pressing the F11 key brings up the Boot Menu, and pressing the F10 key runs the BIOS recovery utility, which you would use if the computer won't boot past the start-up screen, and you can't enter the BIOS because it has become corrupt.

Note that if you see the term CMOS in relation to the BIOS, or even mistakenly used as a term for the BIOS, this stands for complementary metal-oxide-semiconductor. This is the material that the BIOS chip is made of, it is not the chip itself - or any of its contents.

For instance, error messages that the BIOS throws up typically use the term CMOS instead of BIOS. Here is an example - "CMOS checksum error - defaults loaded." This means that the BIOS settings have become corrupt, and the default BIOS settings have been loaded instead of the user's customised BIOS settings.

The bright sparks that program BIOSes probably instinctively want to confuse things as much as possible in order to make what they do as mysterious and as inaccessible as possible.

The BIOS setup program is the first component to start up when you switch a computer on. When the BIOS program runs, it uses a mathematical technique called the "checksum" to make sure the code it contains is sound. If the code fails to pass the checksum test, the BIOS reverts to using its built-in default settings. The default settings can often get the system going again, but the system date and time may be incorrect. Nothing serious because those settings can be set manually from within the BIOS setup program itself. But if the default settings are loaded, any customisation of the settings will be lost and will have to be reset.

Note that whatever fault caused the BIOS to become corrupt will probably still be present, so if you have saved the BIOS settings with a utility that can do so and you restore them, the fault will probably cause the checksum error to recur and wipe them out again.

A bad system crash or electrical spike can corrupt the BIOS file, but this is rare. The most common cause of this kind of error is a dead or dying BIOS battery.

A CMOS-based BIOS chip is a low-power device, but it still has to be supplied with power in order to retain its settings when the computer is switched off. Incidentally, the battery also powers the system clock, which is usually part of the BIOS chip circuitry. When the BIOS battery - usually installed on the motherboard - loses enough of its charge - usually when it is somewhere between three and five years old - the BIOS will not be able to retain its settings, or the code will become corrupt and unusable, and a checksum error will be reported.

Therefore, the first diagnostic step to take to deal with a checksum error is to replace the battery. Most computers use a standard, coin-shaped BIOS battery mounted on the motherboard. You can find a replacement at any good computer shop. Just remove the old one carefully by inserting the flat head of small screwdriver in where the battery makes contact with its socket's metal connector. Take the old battery with you, and show it to the salesman so that you are assured of being given the correct replacement.

If a new battery doesn't solve the problem, the BIOS chip may need to be reflashed, reprogramed, or replaced. The process of reflashing a BIOS chip is provided in this article. But the BIOS chip can be completely reprogramed with special EPROM-programming software that can be purchased an used, or used on your behalf by a professional. A service available from sites such as and, which also provide replacement chips.

A replacement chip will probably cost almost as much or more than a new motherboard, so I personally would replace the motherboard if the BIOS chip cannot be restored to working order.

Also try using the web search term bios checksum error - or any other BIOS term. You'll probably be presented with a large number of accessible links.

How to fix a fast Windows clock problem

If the clock in Windows is fast, try resetting the BIOS to its default settings, because Windows takes its time from the BIOS clock. Doing that often fixes the problem. A fast clock can be a nuisance if you use a PC with a TV tuner card and schedule it to record TV programmes. The BIOS has programming in it that manages the clock's operation.

The BIOS component in a computer stores the hardware configurations that are needed to configure the system at start-up so that its hardware (and thus its software) can run. Many modern BIOSes are also capable of monitoring motherboard activities such as the processor's temperature, the processor's fan speed, and the voltages. The configuration information, in read-only form on a ROM chip, is kept alive by a battery when the system is switched off.

If the battery is removed, the user's customised settings will be deleted as soon as the CMOS chip loses its source of power, which could take several minutes, and the computer will start up with the default or failsafe settings. The user will have to re-enable any settings you prefer to the default ones.

The BIOS also supports software, such as a particular operating system. For instance, a BIOS update may be required before a computer with a BIOS created to run on Windows 98 can be run on Windows XP.

The long-life battery, which lasts at least five years, is usually a round one inserted into a holder on the motherboard, or an external battery unit that is plugged into the motherboard.

The BIOS setup program is accessed by pressing the key or keys shown (usually at the bottom of the screen) just after the memory count at start-up.

The Delete key ("Press DEL to enter SETUP"), used by Award and AMI BIOSes, is the most commonly used one.

See the image below of a start-up screen indicating at the top of the window that the system is configured by an Award BIOS. The BIOS has not recognised the system's AMD Athlon XP 2600+ (Main Processor), because it was released after the BIOS was created. The BIOS will have to be updated by reflashing it with a BIOS file programmed to recognise the new processor.

There is much more information about reflashing a BIOS further down the page.

The Memory Testing feature shows a running count to the amount of RAM used and detected by the BIOS as functional. In this case, it is 512MB (524,288KB). The four headings starting with Primary Master show which of the motherboard's IDE drive channels (used for hard disks or CD/DVD disk drives) have been enabled. The string of numbers and letters shown under Press DEL to enter SETUP can be used to identify the BIOS chip.

Start-up screen showing the RAM memory count, processor, and IDE channels' status

The Press DEL to enter SETUP in the bottom left-hand corner means that you have to press the Delete key to open the BIOS program, and the ALT-F2 to enter AWDFLASH means that you can run the program that reflashes a BIOS update file into the BIOS chip by pressing the ALT and the F2 keys. The BIOS update will have been obtained from the motherboard's website. This means that you can use this utility instead of a special (DOS) boot floppy disk to flash the BIOS.

Below is the much clearer start-up screen showing that the Pentium 4 2800MHz (2.8GHz) processor installed in the system has been recognised by the Award Medallion BIOS. As you can see, the BIOS belongs to an Asus P4T533 - C motherboard (Revision 1007), and has a Maxtor 6L040JZ hard disk drive, and an Asus 52x CD-ROM drive (CD-S520/A ), recognised by the BIOS as being installed as the Primary Master and Primary Slave devices on the Primary IDE channel. There are no drives installed on the Secondary IDE Channel, the Secondary Master setting of which has been disabled, and so displays the word "Skip". The Memory test shows a count of 262,144KB (256MB) of RAM is installed, and has been recognised by the BIOS.

With this BIOS, you still use the Delete key to open it, and the ALT-F2 keys are pressed to run the built-in EZ flash utility, which is used to reflash the BIOS chip with a new BIOS file. This means that you can use this utility instead of a special boot floppy disk to flash the BIOS. The instructions on how to use it will be provided with the BIOS update file, on the motherboard's website, or in the motherboard's user manual.

Start-up screen showing that the Pentium 4 2800MHz processor has been recognised by the BIOS

Below is what appears on the screen at start-up for a computer running an AMI BIOS issued in 1998.

Message on the start-up that provies the information on how to enter the BIOS setup program

And below is the BIOS settings' menu that comes to the screen if the Del key is pressed before Windows, or an alternative operating system such as Linux, starts up. Once the operating system has started loading, you cannot access the BIOS, because it can only make changes to itself when nothing else is loaded. You have to reboot to enter the BIOS when the operating system is running.

AMI BIOS settings menu

Using this particular AMI BIOS, if you suspected that the BIOS settings were responsible for any problems, you would enable the Auto Configuration with Fail Safe Settings option, or even the Auto Configuration with Optimal Settings option.

As long as the start-up screen appears, you can always re-enter the BIOS to change the settings if they don't work or cause problems.

Award BIOSes have similar settings, but pre-year-2000 versions may use terms such as Load Setup Defaults, or Load BIOS Defaults instead of Load Fail-Safe Defaults and Load Optimised Defaults respectively.

Below is the settings' menu of an Award BIOS from the year 2005, which uses similar headings to the AMI BIOS shown above, and which is also entered by pressing the Del key.

The main menu page of an Award BIOS setup program

As I said at the top of this page, you have to navigate using the keyboard, because the driver for the mouse has not been loaded by the operating system. The basic navigation instructions appear at the bottom of the main menu page, and more detailed instructions appear on all of the main pages listed on the main menu page.

For this particular BIOS the important navigation options are:

The important navigation option in the BIOS setup program

The screens, the names for the settings, and the navigation options may differ from one type of BIOS to another, but the content will be more or less the same. It is just a matter of getting used to the differences between, say, an Award BIOS and an AMI BIOS.

BIOS updates: Reflashing the BIOS

BIOS software in the form of a file is flashed into permanent flash memory on the BIOS CMOS chip of a similar kind that is used in flash memory cards. As such, it can be upgraded with a replacement file that provides support for new hardware, or adds new features, or which removes bugs from the installed version. When a BIOS file is updated, it is said to have been reflashed into the flash memory. Visit Page 2 of this article for information on reflashing the BIOS.

Note that most motherboards now allow the user to restore a corrupt BIOS file from a USB flash drive that contains a backup or downloaded BIOS file.

The video/graphics card's BIOS setup program

All video/graphics cards - using a PCI, AGP and PCI Express motherboard slots - have a BIOS setup program that accesses a BIOS chip on the card in the same way as the system's BIOS setup program accesses the BIOS chip built into a computer's motherboard.

At start-up, the main system BIOS detects the video BIOS and adds it to its start-up routine. If you observe the start-up screen, you might be able to see the video card being acknowledged by the system BIOS in the same way as it acknowledges the disk drive(s).

Updates for the BIOS file can be made available for both the motherboard's system BIOS and the video card's BIOS from the motherboard manufacturer's and the video card manufacturer's sites respectively. Instructions on how to update the BIOS are usually also supplied. Often new features can be added by updating a video card's BIOS, because the manufacturer often uses the same video chip on high-end and low-end cards, and it's the BIOS that limits the low-end card. If that is the case, doing nothing more than updating the BIOS can make a low-end card function like its high-end relative. Updating a video card's BIOS can also sometimes solve problems that are otherwise insolvable. But note that you cannot access the settings of the BIOS of a video card as you can access the settings of the motherboard's system BIOS by pressing the entry key(s) at start-up to run the BIOS setup program.

Advanced Guide: Flashing a Video Card BIOS -

The BIOS and overclocking

Click here! to visit the information on this website that deals with the BIOS involvement in overclocking the processor, graphics card, etc.

Note well that you should know what you are doing before you experiment with overclocking a computer.

The overclockability of a desktop or laptop PC's processor depends on the overclocking settings provided by the BIOS and on whether or not the processor is unlocked- does not have its clock multiplier locked so that it can't be changed via the BIOS.

Some motherboard's have BIOSes that are designed for overclocking. For example, the Asus P5E64 WS Professional Socket LGA775 motherboard (for Intel dual- and quad-core processors) has intelligent overclocking settings in its BIOS that allow the user to adjust the voltages of the North Bridge chip, the FSB, the processor, and the RAM memory to achieve the most precise settings to match changes in the settings for the FSB and the clock multiplier.

You can download the user manuals for Asus motherboards from if you want to see the BIOS settings that they provide. The the Asus P5E64 WS Professional motherboard is a good example of one that has been designed with overclocking in mind. MSI also provide good manuals for their motherboards. However, MSI motherboards usually have BIOSes that are restricted to the kind of basic settings the changing of which won't get the user into the kind of trouble that results in high support costs.

A video-card problem problem caused by a buggy BIOS


I found out how easy it is to overlook the BIOS when attempting to diagnose the cause of a computer's problems.

It began when I downloaded and installed the latest driver file for my GeForce 2 video card, obtained from I did so in order to play Deus Ex 2, which requires pixel shading. It's an officially endorsed Windows Hardware Quality Labs (WHQL) driver file, and I had the latest DirectX 9.0c installed, but I soon discovered that the vivid colours of my screensaver were no longer showing.

I decided to buy and install a video card made by MSI with an nVidia 5900ZT chip, but not only did it not fix the screensaver problem, Deus Ex kept on crashing during the boot sequence, and the computer continually rebooted.

Eidos, the maker of the game, told me to do the usual uninstalling of the game, defragmenting the hard drive with the Windows Disk Defragmenter, and reinstalling the game and video-card's driver file, but the blue screen of death and Microsoft's crash analysis both suggested a problem with the driver. MSI, the maker of the video card, provided the same suggestions, but also advised me to reflash the BIOS with the latest file.

The computer has an Asus A8V Deluxe motherboard, so I downloaded the latest BIOS file for the make and model of motherboard from and followed the instructions that were included in the Zip file.

It was a painless operation, and it fixed all of the problems, but I have no idea why it did. Can you enlighten me on the working of the BIOS in this case?


There is a very thin dividing (error) line between providing high performance and system stability with regard to high-end video cards. Indeed, most problems with video cards come about because the driver writers don't get the trade-off right.

Much also depends on the manner in which the video card interacts with the motherboard's chipset. The timings set in the BIOS for the motherboard's chipset are of crucial importance for trouble-free use. The timings have names in the BIOS setup program such as AGP master wait state write, and AGP bus read wait states, which are both applicable to an AGP video card of the kind you were using to begin with and use now.

Windows 95/98/Me/XP all bypass both the video card's own BIOS and the motherboard's BIOS. Windows accesses the computer's hardware directly, but it picks up the timings that are set in the BIOS when the computer first starts up. These timings can often be tweaked in the BIOS itself. One or more of these timings can be the cause of a particular problem such as yours. If tweaking the timing settings is possible, and doing so doesn't solve the problem, reflashing the BIOS with an updated file that has been reprogrammed can often do the trick. In your case it did just that.

Information on how to reflash to upgrade a BIOS is provided on Page 2 of this article.

A faulty BIOS problem: Windows XP, Windows 2000, and Windows 98 won't install on my PC

The following problem was caused by a faulty BIOS:

I have a problem with a PC I am building that has an Asus K8 NE Deluxe motherboard, one module of 512MB of PC3200 DDR RAM, a Sempron 3100+ 64-bit processor, an Antec 350 SmartPower power supply, a 20GB Maxtor PATA IDE hard drive, a floppy drive, and a DVD writer. With the BIOS settings set to default, the PC boots with the Windows XP OEM CD, but the installation only gets to the format drive stage then hangs. It does not start the format. I have tried 3 hard drives, 2 CD drives, 2 floppy drives, loading Windows 2000 Pro, loading Windows 98 SE, same result, and another copy of XP Home Edition, same result. I have another PC that I built with the same equipment, motherboard, and RAM, but with an Athlon 64 3000+ processor and an SATA hard drive. This PC has worked really well from day one. I connected the SATA drive from this PC in the problem PC, with Windows 2000 Pro installed on it, but it only got as far as the Windows 2000 Pro screen with the progress scale complete, then, alas, it stopped. There was an error message that appeared onscreen, I think during a Windows 98 installation, that read as follows: Standard mode bad fault in dos extender, fault,000D stack dump,036c 0000 0070, Raw fault frame,EC,3004 IP 2443 CS=0053 FL3097 SP=00F2 SS004B.

The man who had this problem discovered the cause of it himself:

I decided to clear the CMOS, removed the BIOS battery, reset the jumpers, put it all back as was. This produced some progress, the Windows installation did the format, and I got the Windows screen followed by a stalled blue or black screen. I download a beta BIOS for the motherboard from the Asus website - the latest update. I followed the EZ Flash utility instructions from the manual, flashed the BIOS, and bingo! When I restarted the system it went straight into a clean installation.

Boot sector virus protection: Disable it before installing Windows 95 and Windows 98

When the Virus Warning setting (usually in the BIOS Features Setup menu) is enabled, the BIOS will flash a warning message whenever there's an attempt by a virus (or legitimate software) to access the system's boot sector or its partition table. If present, it is recommended to have this setting enabled. Note that this only protects the system's boot sector and its partition table, not the entire hard disk drive.

However, note well that this feature will cause problems with the installation of certain software. For example, when enabled, this feature will cause the installation routine of Windows 95 and Windows 98 to fail. (It doesn't affect the installation routine of Windows XP.) Therefore, disable it before installing such software. Moreover, many hard disk drive diagnostic utilities that access the boot sector can also trigger the error message. The Virus Warning setting should be disabled before using such utilities.

This BIOS setting is useless for hard disk drives that run from controllers on PCI adapter cards and other external controllers (such as SCSI controllers and UDMA 66 controllers) that have their own BIOS. Boot sector viruses will bypass the system BIOS and write directly to such hard disk drives.

See the Disk Drives section of this website for more information on UDMA (IDE ATA) and SCSI hard disk drives.

The APIC mode BIOS setting

APIC mode (Advanced Programmable Interrupt Controller) is a BIOS setting made available to Windows 2000 and Windows XP systems that increases the number of IRQ (Interrupt Request) lines available to the processor.

When APIC is disabled in a Windows 2000/XP system, only 16 IRQs (0 to 15) are available to the processor, as is the case with Windows 9.x systems, instead of the 23 that are available with this setting enabled. This reduces the amount of hardware that can be run on the system to the level of Windows 9.x system, and can therefore be the cause of unnecessary hardware conflicts.

You can examine the allocation of the IRQs in the Device Manager. In a Windows 9.x system you do that by double-clicking the Computer heading at the top of the window.

To access the Device Manager in Windows XP, Windows Vista and Windows 7, enter devmgmt.msc in the Start => Run box in XP and the Start => Search box in Vista/Windows 7.

Always update the BIOS before making a major change of operating systems

If you are planning to change your operating system from say Windows 98 SE to Windows XP ( a major change), save yourself a lot of hassles by checking the motherboard/PC manufacturer's website for a BIOS update. A large percentage of operating-system upgrade problems would be avoided just by reflashing the BIOS with the latest update file.

But you probably wouldn't have to take that action if you changed from Windows 98 to Windows 98 SE, because that is not a major change. Both versions of Windows 98 use the same architecture, but Windows XP uses a totally different architecture. It is not considered a major change to upgrade from Windows XP to Windows Vista, because the architecture of both versions is similar.

If you cannot obtain a BIOS update for the existing motherboard, try making the changeover, or dual-boot Windows 98 and Windows XP to experiment safely, but if it doesn't work out, you will probably have to install a new motherboard with a BIOS that supports Windows XP if you want to use it as the operating system. And given how fast technology is changing, you will almost certainly have to purchase new RAM, and a new processor for that motherboard, because the RAM and processor on the old motherboard won't be compatible with the new motherboard. And if you choose an Intel Pentium 4 (Socket 478) motherboard over an AMD (Socket A) motherboard, you will also have to purchase a new case, because Pentium 4 motherboards require a special power-supply unit and special case mountings. But if you choose an AMD solution, you will be at least be able to reuse an ATX case if the existing power-supply unit meets the processor's power requirements. (Check AMD's website for recommended cases and power supplies.) If not, they you will just have to install a new power-supply unit into the case.

Click on the following link of the Build Your Own PC section on this website for information on how to install a power supply. That section of this website provides information on installing all of the other components.

A multi-language BIOS

Some new motherboards, such as those made by Asus, provide a BIOS that supports several different languages. The extract below is from the user manual of the Asus A8N-E Socket 939 motherboard for AMD Athlon 64 processors.

Asus Multi-language BIOS

BIOS battery replacement: How to replace the BIOS (CMOS) battery

Motherboard battery

Note that desktop and laptop PCs now store the EFI settings in non-volatile permanent memory that retains information when the PC is switched off, which means that the EFI does not require to make use of a battery supplied by the PC's motherboard to retain its data. However, motherboards still have a battery because the Real Time Clock (RTC) that keeps date and time information has to be powered. The operating system takes its date and time from the RTC. The EFI is not accessed by pressing an entry key (Del, F1, etc.) at startup, it is accessed from within Windows 8.1 and higher versions of Windows.Close-up view of a Sony BIOS battery and the BIOS chip on a motherboard

The image above shows a close-up view of a Sony BIOS (CMOS) battery in its socket on a motherboard. The BIOS chip is next to it. For the battery installation the desktop of laptop PC's motherboard, there are three types of battery socket types. The following webpage shows how to replace all three types. -

This Q&A on this site deals with the problem that its title describes: Why is my computer running slow after I replaced a flat BIOS battery on the motherboard?

I need to replace the motherboard's BIOS battery, but I don't want to reset my customised/customized settings


I need to replace my motherboard's BIOS battery, but I don't want to have to reset my customised settings, so can anyone recommend a program that will save the settings so I can restore them after I replace the battery?


The flash utility that can be used to reflash a BIOS, if its motherboard manufacturer provides one from its website, can usually save the old BIOS file so that it can be restored if reflashing the BIOS causes a problem. You can obtain it with the latest BIOS update for a make and model of motherboard from the motherboard manufacturer's site.

Some motherboard manufacturers provide a utility that can save, manage and update the BIOS. Here is one form Asus that has to be used with an Asus motherboard. Have a look on to find out if there is a more recent update, because this one from Major Geeks is dated June 19, 2007. It probably won't work to update the new type of EFI BIOS.

You could also take digital photos of each of the BIOS pages to save the customised settings. This is the easiest and safest way. You shouldn't mess around with the BIOS unnecessarily, because if it gets corrupted, the PC will be rendered unbootable and if the BIOS can't be recovered by reflashing it or installing a new BIOS chip, a new motherboard would be required.

BIOS CMOS checksum error on startup


Three days ago, the following error message started presenting itself whenever I switch on my desktop PC: "CMOS checksum error - Defaults loaded. Press F1 to continue, Del to enter Setup". When I press F1, the PC starts up as usual, but the clock shows 0.00, and in the Control Panel's Date & Time, the date is always January 1 2003.


It looks as if you have to replace the BIOS battery that powers the CMOS chip that contains the clock's settings. The chip stores the BIOS settings in the same way that a mobile phone stores its settings. If you remove the battery in a mobile phone or it runs out of charge, the settings are lost. The chip also stores the customised BIOS settings, so the computer has to load the default settings, which are hard-coded into it so that they are always accessible to the startup process - even when the BIOS battery is flat.

The image above this table shows a Sony BIOS battery installed in its socket on the motherboard. The BIOS battery is rechargeable, recharging while the computer runs. After four or five years, it stops taking a charge and has to be replaced. If the PC hasn't been used for a few weeks or months, the battery may still be working but may just have run down. Leaving the PC on for a day should recharge it.

Most of the motherboards of desktop PCs currently in use have a jumper that clears the CMOS settings when it shorts two specific pins, the blue object in the centre of the image below that also shows the BIOS/CMOS battery in its container on the left of the jumper.

Showing the jumper that  clears the BIOS/CMOS chip when set to do so across two specific pins

The motherboard's manual shows the jumper's location on the motherboard. You can identify the motherboard's make/model with a utility such as CPU-Z and then locate its manufacturer's site with a search engine. The motherboard manufacturer's site should provide a manual for that model. The jumper is near the BIOS battery and is often labelled as such.

If that jumper is left in the 'clear' position or is missing, the computer will produce that checksum error message.

Brand new motherboards can have the jumper set to clear the BIOS in order not to run the battery down. Many people don't bother reading the manual and so are not made aware of that fact.

Motherboard manufacturer's warning

Note well: I came across the following warning in the motherboard manual for an MSI K8N Neo4 Platinum/SLI Socket 939 motherboard. Until then, I wasn't aware of the danger:

"Caution. Danger of explosion if [BIOS] battery is incorrectly replaced. Replace only with the same or equivalent type recommended by the manufacturer."

Rechargeable CMOS/BIOS batteries

Some new CMOS batteries are rechargeable and therefore shouldn't need to be replaced. The motherboard's manual would specify that the battery is rechargeable if it is. The battery is charged while the computer is running. So, if the computer hasn't been used for a while, and the system loads with the BIOS defaults settings, it would be because the CMOS battery has run down. Keeping the system running for a while should recharge it and allow you to customise the settings so that they remain every time the computer boots.

How to reset the BIOS itself and how to reset the BIOS password

How to reset the BIOS itself

In a desktop PC, there is almost always a Reset CMOS jumper on a motherboard that can be set to activate or clear the BIOS settings.

Click here! to see an illustrated extract on this website of where a reset jumper is located on the motherboard and how to set it taken from an MSI motherboard's manual.

Some motherboard manufacturers are now providing a Reset/Clear CMOS button on the motherboard's ports panel as shown in the next image of an MSI motherboard below.

The option to reset the entire BIOS itself to its default settings must not be confused with its Reset Configuration Data setting that resets the hardware configurations. When that setting is enabled, the BIOS resets not itself but what it knows about all of the hardware components and peripheral devices (printers, etc.) and then it disables the option. All of the existing hardware configuration data is erased and then replaced, giving a fresh start that can resolve many hardware misconfiguration problems.

However, is different in laptop PCs because of their highly-integrated designs which make accessing the motherboard so difficult that only trained technicians should attempt doing so. If you want to reset the BIOS of a laptop PC, read the item at the end of this section on resetting the BIOS.

However, the situation of resetting the BIOS itself (not its configurations of components and devices) is different in laptop PCs because of their highly-integrated designs which make accessing the motherboard so difficult that only trained technicians should attempt doing so. If you want to reset the BIOS of a laptop PC, read the item at the end of this section on resetting the BIOS.

It might be necessary to make use of the reset-BIOS feature if you have set incompatible BIOS settings that can render the computer unbootable - or something else has gone wrong with the settings. Only the current BIOS settings that the computer has been using are cleared by using the reset-CMOS jumper setting, not the main BIOS settings, which are permanently placed into flash memory when the BIOS's CMOS chip is flashed. (The CMOS chip can be reflashed with an updated file.) Unlike the RAM memory that holds customised settings, flash memory retains data without being powered. The reset jumper setting cuts the power from the CMOS battery to the CMOS chip that holds the BIOS settings, thereby removing them. When the PC starts up and tries to access the BIOS settings, it finds none (if the BIOS has been cleared) and it makes the BIOS copy the default settings from the flash memory into the RAM memory area that is usually kept alive by the BIOS battery. To keep customised BIOS settings, the jumper has to be placed over the two pins that allow power to go to the CMOS chip.

The BIOS settings are also cleared if the battery is disconnected for about five minutes.

Note that some motherboard manufacturers have the Reset CMOS jumper set to disabled in order to disconnect the BIOS battery so that it doesn't run down during storage.

If this is the case, having installed the motherboard, you would have to set the jumper setting to activate the BIOS, or you would have to reset any customised BIOS settings (you have enabled or disabled in preference to the default settings) every time the computer boots. The computer would boot if the CMOS jumper is set to clear the BIOS, but the default BIOS settings will be loaded and used every time the computer boots.

The following page provides illustrated information on how to reset the BIOS:

Pressing a button on the motherboard or on its ports panel to clear the CMOS chip's BIOS settings

The motherboard manufacturer MSI is familiar with the problems that are caused by overclocking, so now it includes a Clear CMOS button on the main face of many of its motherboards or on the ports panel. The MSI MS-7673 Intel-based Socket 1155 motherboard, the ports panel of which is shown below, has a Clear CMOS button. If the button is on the motherboard itself, it is next to the BIOS CMOS chip and battery. Press the button to reset (clear) the BIOS so that it uses its default settings the next time the system is started up. This can be done without having to open the case with an external button if, say, conflicting BIOS settings are enabled by the user that render the computer unbootable.

Ports panel of an MSI MS-7673 Socket LGA1155 Intel-based motherboard

The motherboard's manual will have diagrams that show where all of the different components, connectors, jumpers, and those buttons are located.

Some motherboards provide a secondary plug-in BIOS chip

If you have a very recent motherboard, it may come with a secondary BIOS chip that plugs into the board and overrides the BIOS chip that is fitted to it. If that is the case, you just have to plug the secondary chip into its socket in order to recover the BIOS. An example of such a motherboard is the ECS KA3 MVP, a Socket AM2 board that runs AMD Athlon 64, 64 FX, and 64 FX X2 dual-core processors.

How to reset the BIOS password

If you've made use of the Set Supervisor Password and/or the Set User Password options and you forget the password(s), or just want to disable having to enter one or both of them, the computer's motherboard has a jumper setting that can be set to clear the password(s). You have to consult the motherboard's manual to find out how to set the jumper. If you don't have a manual, identify the motherboard's manufacturer and download a copy from its website for that make and model of board.

How to reset the BIOS password in a Dell desktop PC

Apparently it is difficult to reset the administrator/supervisor password in the BIOS of a Dell PC. If the information isn't provided in the PC's user manual, ask Dell's technical support for information on how to do it, and read this thread for more information:

Dell BIOS admin password removal -

How can I reset the password-protected BIOS in a Samsung R40Plus laptop PC?


I have a Samsung R40Plus laptop PC running Vista Home Premium, and want to replace it with Windows XP Professional, but the BIOS setup program is password-protected and the password is not mentioned anywhere in the documentation. Is there any way onboard of re-setting the BIOS?


In a desktop PC, you would consult its user manual of its motherboard to locate the jumpers the pins of which are used to activate or reset the BIOS, but that can't be done easily with laptop PCs because of their highly integrated designs. In fact, it is advisable not to attempt to reset the BIOS of a laptop. Instead, make use of software that cracks the password.

CmosPwd decrypts the password stored in CMOS BIOS chip used to access the BIOS Setup Program. -

BIOS settings and information provided by the motherboard's manual

Note that the motherboard manual - that comes with a new PC or can usually be downloaded from the motherboard manufacturer's website - usually has a section in it devoted to the BIOS settings. The information provided is usually brief and inadequate. The settings of each menu page are named, a brief description of the purpose of each setting is provided along with if it is the a default setting or one that can be enabled if the user chooses.

Inadequate BIOS information has resulted in numerous BIOS websites aimed at meeting the need for more detailed information.

Note that should you experience difficulties with the IRQ assignments of the devices that appear in the Device Manager, you can enable the Reset Configuration Data setting. This will reassign the IRQs just once and then disable itself. If you are having IRQ assignment problems with a device and you want the BIOS to configure the devices instead of Windows as a way around the problem, disable the PnP OS setting and enable the Reset Configuration Data setting.

If you want to view the 16 IRQ assignments in a Windows 9.x system, double-click the top Computer heading in your computer's Device Manager.

The computer assigns a device or collection of devices (IRQ sharing) an IRQ line so that each device can request attention from the processor. Since there are only 16 IRQ lines available, and most of them are reserved, when adding a device you may run into an IRQ problem, and then have to find a way to free an IRQ line for the device. This is usually done by removing unused devices (such as one or both of the COM ports) and disabling them in the BIOS.

Using the BIOS ID number or free utilities to identify a motherboard in order to be able to upgrade its BIOS

If you upgrade the BIOS for particular make/model of motherboard, you have to identify the BIOS so that you upgrade that BIOS with the update written t update it. If you use an update designed for another make/model of motherboard, the computer can be rendered unbootable.

Every Award and AMI BIOS has a unique ID number, a string of numbers and letters that usually appears briefly at the bottom left-hand side of the standard screen at start-up (that is not the motherboard manufacturer's logo screen). If the first screen displays the manufacturer's logo, you have to enter the BIOS to enable the setting that displays the standard startup screen. To make a note of the number, use the Pause key to freeze the screen. Wim's BIOS site provides the information on how to decode BIOS ID numbers.

Luckily, there are several excellent free utilities that you can download and run that identify a computer's hardware and software, including the BIOS ID number, such as the free Belarc Advisor.

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