What Is UEFI, and How Is It Different from BIOS? – How-To Geek

The BIOS will soon be dead if it isn’t already: In 2017, Intel announced plans to completely replace it with UEFI across all of its chipsets, and the industry quickly followed suit. But what is UEFI and how is it different from the BIOS we’re all familiar with?

Both UEFI and

BIOS are low-level software that starts when you boot your PC before booting your operating system, but UEFI is a more modern solution, supporting larger hard drives, faster boot times, more security features, and, conveniently, graphics and mouse cursors.

We’ve seen that newer PCs

that ship with UEFI still refer to it as the “BIOS” to avoid confusing people who are used to a traditional PC BIOS. Even if your PC uses the term “BIOS,” the modern PCs you buy today almost certainly ship with UEFI firmware instead of a BIOS. Here’s why.

What is a BIOS?

RELATED: What Does a PC’s BIOS Do and When Should I Use It? BIOS

is short for Basic Input-Output system. It is low-level software that resides on a chip on your computer’s motherboard. The BIOS is loaded when the computer starts, and the BIOS is responsible for activating the hardware components of the computer, making sure they work properly, and then running the boot loader that boots Windows or any other operating system that you have installed.

You can configure various settings on the BIOS setup screen. Settings such as your computer’s hardware configuration, system time, and boot order are located here. You can access this screen by pressing a specific, different key on different computers, but often Esc, F2, F10 or Del, while the computer starts. When you save a configuration, it is saved in the motherboard’s memory. When you start your computer, the BIOS will configure your PC with the saved settings.

The BIOS goes through a POST, or self-test power-on, before booting the operating system. Verify that the hardware configuration is valid and working correctly. If something is wrong, you’ll see an error message or hear a cryptic series of beep codes. You’ll need to look up what the different beep sequences mean in your computer’s manual.

When the computer starts, and after the POST is complete, the BIOS looks for a master boot record, or MBR, stored on the boot device and uses it to start the boot loader.

You can also see the acronym CMOS, which stands for Complementary Metal-Oxide-Semiconductor. This refers to battery backup memory where the BIOS stores various settings on the motherboard. In reality, it is no longer accurate, as this method has been replaced by flash memory (also known as EEPROM) in contemporary systems.

Why the BIOS

is outdated

The BIOS has

been around for a long time and hasn’t evolved much. Even MS-DOS PCs released in the 1980s had a BIOS!

Of course, the BIOS has evolved and improved over time. Some extensions were developed, including ACPI, the advanced configuration and the power interface. This allows the BIOS to more easily configure devices and perform advanced power management functions, such as sleep. But the BIOS hasn’t advanced and improved as much as other PC technologies since the days of MS-DOS.

The traditional BIOS still has serious limitations. It can only boot from drives 2.1 TB or less. 8TB drives are now common, and a computer with a BIOS can’t boot from them. That limitation is due to the way the BIOS Master Boot Record system works.

The BIOS must run in 16-bit processor mode and has only 1 MB of space to run. You have trouble initializing multiple hardware devices at once, which leads to a slower boot process when initializing all interfaces and hardware devices on a modern PC.

The BIOS has needed replacement for a long time. Intel began work on the Extensible Firmware Interface (EFI) specification in 1998. Apple chose EFI when it switched to Intel architecture in its Macs in 2006, but other PC makers didn’t follow.

In 2007, Intel, AMD, Microsoft, and PC manufacturers agreed on a new Unified Extensible Firmware Interface (UEFI) specification. This is an industry-wide standard managed by the Unified Extended Firmware Interface Forum and is not powered solely by Intel. UEFI support was introduced in Windows with Windows Vista Service Pack 1 and Windows 7. The vast majority of computers you can buy today now use UEFI instead of a traditional BIOS.

How UEFI replaces

and improves


UEFI replaces the traditional BIOS on PC. There is no way to switch from BIOS to UEFI on an existing PC. You should buy new hardware that supports and includes UEFI, as most new computers do. Most UEFI implementations provide BIOS emulation so you can choose to install and boot older operating systems that expect a BIOS instead of UEFI, so they are backward compatible.

RELATED: What’s the Difference Between GPT and MBR When Partitioning a Drive?

This new standard avoids BIOS limitations. UEFI firmware can boot from drives of 2.2 TB or larger; In fact, the theoretical limit is 9.4 zettabytes. That’s about three times the estimated size of all data on the internet. This is because UEFI uses the GPT partition scheme instead of MBR. It also boots in a more standardized way, starting EFI executables instead of executing code from a drive’s master boot record.

UEFI can run in either 32-bit or 64-bit mode and has more addressable address space than the BIOS, which means the boot process is faster. It also means that UEFI setup screens can be sleeker than BIOS setup screens, including graphics and mouse cursor support. However, this is not mandatory. Many PCs still ship with text-mode UEFI configuration interfaces that look and function like an old BIOS setup screen.

UEFI is packed with other features. It supports Secure Boot, which means that the validity of the operating system can be checked to ensure that no malware has altered the boot process. It can support networking directly in UEFI firmware, which can help in remote troubleshooting and configuration. With a traditional BIOS, you have to be sitting in front of a physical computer to set it up.

It’s not just a BIOS replacement either. UEFI is essentially a small operating system that runs on top of PC firmware, and it can do much more than just a BIOS. It can be stored in the motherboard’s flash memory, or it can be loaded from a hard drive or network share at boot.

Different UEFI PCs will have different interfaces and features. It all depends on your PC manufacturer, but the basics will be the same on every PC.

RELATED: How to Check If Secure Boot Is Enabled on Your PC How

to Access UEFI Settings on Modern PCs If you’re a normal PC user, switching to a computer with


won’t be a noticeable change. The new computer will boot up and shut down faster than it would with a BIOS, and you can use drives 2.2 TB or larger in size.

If you need to access low-level settings, there may be a slight difference. You may need to access the UEFI settings screen through the Windows boot options menu instead of pressing a key while your computer starts. With PCs now booting up so fast, PC manufacturers don’t want to slow down the boot process by waiting to see if you press a key. However, we’ve also seen UEFI-enabled PCs that allow you to access the BIOS in the same way, by pressing a key during the boot process.

While UEFI is a great upgrade, it’s largely in the background. Most PC users will never notice, or need to worry, that their new PCs use UEFI instead of a traditional BIOS. They will simply perform better and support more modern hardware and features.

For more detailed information, read Red Hat’s Adam Williamson’s explanation of how the UEFI boot process is different. You can also read UEFI’s official FAQ.

Image credit: Wikimedia Commons