The BIOS handles the startup process and overall management of the PC. In this video, you’ll learn about the BIOS startup process, the difference between a legacy BIOS and a UEFI BIOS, and much more.
The BIOS of your computer is the Basic Input Output System. It’s the firmware or the software that’s used to get your computer running. Sometimes you’ll hear this referred to as the system BIOS or the ROM BIOS. The term ROM BIOS refers back to the days when this software was stored on Read Only Memory chips that were on the motherboard.
Our modern computers store this BIOS software in flash memory, so we’re able to upgrade the BIOS by using an application rather than removing chips and replacing chips on the motherboard. When you first turn your computer on, the BIOS initializes the memory and performs a check of your system. This check is called a Power On Self-test or a POST.
The POST process will look for a CPU, for memory, will check to see that you have a display connected and a keyboard. And if all of the hardware passes these diagnostics, it then begins to look for a boot loader on a storage device to load the operating system. If you look closely at your motherboard, you’ll probably be able to find the flash memory that holds that BIOS software.
In this particular motherboard, there is a main BIOS and then there’s a backup BIOS. This allows you to easily perform upgrades to the BIOS and then be able to switch back and forth between different BIOS versions. There are two different types of BIOS that you might find on a computer.
The first is what we call a legacy BIOS. This is the BIOS that’s been around for well over 25 years. Older operating systems would communicate through this BIOS to gain access to the hardware of the computer. This legacy BIOS was designed for an older type of hardware.
So access to USB interfaces, network interfaces, or some of our modern storage devices wasn’t possible through a legacy BIOS. A much more common BIOS these days is the UEFI BIOS. This stands for Unified Extensible Firmware Interface, and it’s based on a BIOS type that Intel created called the EFI BIOS. This standard was created so that all of the motherboard manufacturers could use a standard type of BIOS across every single manufacturer.
These UEFI BIOS is designed to completely replace the legacy BIOS and it provides support for all of our modern hardware. You might also find a more graphical front end, which makes it a little bit easier to use. But there are options to also use a text-based front end as well. The UEFI BIOS brings with it a number of advantages.
One is that it’s able to boot from very large drives that are over 2.2 terabytes in size that have been formatted with the GUID partition table. That’s the globally unique identifier. You may sometimes see this referred to as GPT disks. UEFI BIOS can also boot from File Allocation Table or FAT formatted drives, and it does support removable media as well so you can boot from a USB flash drive.
From a troubleshooting perspective, one of the advantages of UEFI BIOS is that we have a pre-boot environment. You can think of this as a mini operating system that has its own drivers, its own shell. We can run applications.
This allows us to browse the internet, backup drives that are on the system, be able to access the network all without booting a full-blown operating system. We can do this all from the UEFI BIOS. When you make changes to the BIOS configuration, you need somewhere on your system to store those changes. Those changes are stored in non-volatile BIOS memory. This memory is usually flash memory that’s on the motherboard that stores all of our BIOS configuration settings.
Before we had flash memory to store these BIOS configuration settings, we stored everything on Complementary Metal Oxide Semiconductors or CMOS. The CMOS allowed us to write and then change the information on the CMOS, and then there was a battery on the motherboard that made sure that that information was constantly refreshed so we didn’t lose our configurations. These days, of course, we have flash memory and our BIOS configurations are stored on flash, which means we don’t have to have a battery or constantly provide power to maintain those configurations.
Even though we’re using this flash memory these days instead of CMOS, you’ll still hear people refer to that configuration setting area as the CMOS or the CMOS settings. When we refer to the CMOS today, we’re really referring to the data that we’re storing into flash memory that contains the BIOS configuration settings. If you look closely at the motherboard of your computer, you’ll probably see there is a battery on the motherboard. On this particular motherboard, it’s right next to the CPU.
Since we’re not using CMOS to store a BIOS configuration settings, this battery is most commonly used to maintain the data and the time on this computer. These batteries can last for years. But if the battery does lose its charge, you’ll find that your computer is not able to maintain the date and time if you happen to remove the power from your computer.
Since the battery on our older CMOS systems was designed to maintain the BIOS configurations if you simply remove the battery, then you’re also clearing out all of the BIOS configurations including any passwords that might have been used for supervisor access. On these newer motherboards, there’s usually a jumper that you’ll connect, power on the system, and that jumper would tell the flash memory to clear out all of your BIOS configurations.