What are the BIOS, CMOS, and UEFI?

BIOS stands for basic input/output system. The BIOS is firmware that’s built into the motherboard that initializes the computer’s hardware as the computer is being booted. then after it initializes the hardware, it then searches for a boot device, like an optical drive or a storage drive, else software like an OS. So, from the beginning, when you first turn on the pc, the pc does what’s called a power-on self-test or POST,

Which is run by the BIOS. It tests the pc to make sure all the requirements are met and if the hardware is functioning correctly before starting the OS. If the pc passes the test, the internal speaker will make a short single beep which indicates that the pc has passed the test and is booting up normally. However, if there are no beeps or multiple beeps then meaning that the pc has failed the test and something is wrong and therefore the computer needs further troubleshooting to find out what the problem is.

So, whether there are not any beeps or multiple beeps, the computer will generate a beep code to assist you to pinpoint the matter. So, for example, if the computer generates three long beeps, then that would indicate a keyboard error. Or if the pc generates endless short beep, then that would indicate a tangle with a RAM module. So whatever BIOS is installed on the computer’s motherboard, you’ll always ask the manufacturer’s documentation to seek out a list of beep codes and what they mean so you’ll pinpoint the matter and correct it. The BIOS software is stored on the BIOS chip on the motherboard. The BIOS chip is non-volatile, which means that the contents of a chip are retained even after the power is turned off. But even after the pc is turned off, the pc does need to maintain certain settings, such as the date and time, the boot sequence, and certain hardware settings. In other words, the custom settings that you have configured in the BIOS. And these settings are stored on the motherboard in a special chip called a CMOS chip. But unlike the BIOS chip which is non-volatile, the CMOS chip is volatile. Meaning that it needs constant power to maintain its contents or settings. So as for the CMOS to maintain its settings while the pc is turned off, it uses A battery. And this battery is named the CMOS battery.

The CMOS battery is a small button cell battery that will be seen on the surface of the motherboard and it’s always located on the bottom right-hand corner. And it’s basically an equivalent type of battery that’s typically used in wristwatches. Now as I stated before, the CMOS needs constant power that’s supplied by the battery. But if the battery is removed and then reattached, the BIOS will reset back to its default settings from the manufacturer and erase any custom settings that you simply have configured.

Now tons of people get confused about what is the difference between BIOS and CMOS. And these terms are often wont to ask an equivalent thing, but they’re different. So just to clarify things, the BIOS is the actual firmware or program that comes together with your motherboard. and that firmware is stored within the BIOS chip. But the settings that you simply actually make to the BIOS, such as a date and time, the boot sequence, fan speeds, and things like that, those settings are retained within the CMOS chip.

Now the CMOS chip is not necessarily its own chip. On modern motherboards, it’s been integrated with the real-time clock that’s part of the southbridge chipset.

BIOS,CMOS,UEFI, What are the BIOS, CMOS, and UEFI?, TechRX

Now a replacement sort of BIOS is named UEFI. UEFI stands for unified extensible firmware interface. Now, most if not all new motherboards are shipped with this newer type of BIOS. UEFI has several advantages over the old BIOS. and therefore, the first and most blatant, just by looking at it, is that it’s a user-friendly graphical interface that supports different colors and even animations. Whereas the old BIOS has your typical blue screen that resembles the windows blue screen of death. UEFI also can recognize larger storage drives and you’ll even use a mouse within the UEFI interface, whereas compared to the old BIOS, where mouse support wasn’t even available and you had to use your keyboard only. And UEFI also has a built-in feature called secure boot.

And secure boot stops any digitally unsigned drivers from loading and it also helps to stop malicious software such as rootkits.


  • BIOS,CMOS,UEFI, What are the BIOS, CMOS, and UEFI?, TechRX

    My name is Biplab Das. I’m the leader of TechRX and Founder of Blendservers.com and helloIPz.com Professionally I'm a full-time IT support engineer whose childhood obsession with science fiction never quite faded. A quarter-century later, the technology that I coveted as a kid is woven into the fabric of everyday life. People say smartphones are boring these days, but I think everyone is beginning to take this wonderful technology marvel for granted.

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