Briefly Introduce the BIOS & UEFI
In the previous discussion, the author mentioned UEFI when he set up ubuntu. But I want to know more about how UEFI process on my PC, so I decided to write this article to explain UEFI.
What is UEFI？
UEFI(Unified Extensible Firmware Interface) is a firmware interface that defines the architecture of the platform firmware used for booting and its interface for interaction with the operating system.
Before we talk about UEFI, we must introduce the relationship between BIOS and UEFI first.
BIOS and UEFI
BIOS(Basic Input-Output system) is a firmware that provides runtime services for operating systems and programs, performing hardware initialization during booting. BIOS first appeared in 1975. With the evolution of time, new technological hardware became more complex and required more ROM or storage for booting and initializing the devices. Still, with its limitation, BIOS operates in 16-bit instead of 32/64 bits mode. Its partitioning MBR can only support up to 2 TB storage devices, and these reasons make BIOS hard to survive nowadays. Instead, people need brand-new firmware to solve these problems.
In contrast, UEFI provides a graphical user interface(GUI) that is much easier than the text user interface of BIOS, making users easily control or modify system settings, like adjusting the booting sequence, overclocking the CPU, and so on.
Basically, BIOS and UEFI are doing the same thing — connecting a computer’s firmware to its operating system. UEFI is the first program that runs when users press the power button; then, it will check all the components which are attached, wake the components up and hand them to OS.
The following chart compares the difference between BIOS and UEFI. The most important thing is that UEFI can provide backward compatibility with BIOS using CSM(Compatibility Support Module) booting. In some cases, the device can’t support UEFI mode and only can operate under BIOS mode. They could enable Legacy mode to simulate BIOS in UEFI firmware.
To see more details about the differences between BIOS and UEFI, you can visit these websites.
UEFI Boot Procedure
- Power-on self-test (POST): When you turn on your computer, the UEFI firmware runs a series of diagnostic tests to ensure that the hardware is functioning properly. This is called the POST process.
- Boot Manager: Once the POST process is complete, the UEFI firmware hands off control to the Boot Manager, which is a small program that is stored in a special partition on your hard drive. The Boot Manager presents a menu of boot options, such as different operating systems or bootable devices like USB drives or DVDs.
- Boot Loader: Once you select a boot option from the Boot Manager, the UEFI firmware loads a boot loader program from the selected boot disk partition. The boot loader takes over the boot process and loads the operating system kernel into memory.
- Operating System: The UEFI firmware continues to provide services to the operating system, such as hardware initialization and configuration, even after loading the operating system.
Conclusion
UEFI is the bridge between the operating system and all the attachments in the computer, and it plays an important role while starting up a computer. With more safety processes and containing a bootloader itself, UEFI makes all the processes more efficient and faster than BIOS.
