BIOS, CMOS, UEFI - What's the difference?

What is the BIOS, CMOS, and UEFI? So that's what  we're going to talk about in this video. Now 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. And then after it initializes the hardware, it then searches  for a boot device, such as an optical drive or a storage drive, to boot software such  as an operating system. So from the start, when you first turn on the computer, the computer  does what's called a power-on self-test or POST, which is run by the BIOS.

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

So whether there are no beeps or multiple beeps, the computer will generate a beep code to help  you pinpoint the problem. So for example if the computer generates three long beeps, then  that could indicate a keyboard error. Or if the computer generates a continuous short beep,  then that could indicate a problem with a RAM module.

So whatever BIOS is installed on the  computer's motherboard, you can always refer to the manufacturer's documentation to find  a list of beep codes and what they mean so you can pinpoint the problem 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 computer is turned off, the computer 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 in  order for the CMOS to maintain its settings while the computer is turned off, it uses a battery. 

And this battery is called the CMOS battery. The CMOS battery is a small button cell  battery which can be seen on the surface of the motherboard and it's usually located on  the bottom right hand corner. And it's basically the same type of battery that is typically  used in wristwatches.

Now as I stated before, the CMOS needs constant power that is 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 have configured.  Now a lot of people get confused about what's the difference between the BIOS and CMOS.

And these  terms are often used to refer to the same thing, but they are different. So just to clarify  things, the BIOS is the actual firmware or program that comes with your motherboard. And  that firmware is stored in the BIOS chip.

But the settings that you actually make to the BIOS,  such as a date and time, the boot sequence, fan speeds, and things like that, those  settings are retained in 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.

Now a new type of BIOS is called 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 the first and most obvious, just by looking at it, is that it has a user-friendly graphical  user 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 can also  recognize larger storage drives and you can even use a mouse in 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.