Step 5: The Kernel Phase

The last step is for the bootloader to load the OS (the Linux kernel). The kernel then sets the stage for the rest of the OS initialization process. The post-kernel processes remain the same for UEFI as that for BIOS.

UEFI vs. BIOS

Modern PCs use UEFI firmware because it supports hard drives beyond 2TB, boots more quickly, and has better security features. UEFI is better than BIOS. However, not all motherboards support it. Many cheaper motherboards still implement BIOS configuration. Also, the initialization of UEFI firmware platforms follows a defined approach. By doing so, UEFI firmware modification becomes independent of any specific manufacturer [7].

For the UEFI-specific platform, the firmware doesn't need to worry about initializing the devices that play a more hands-on role in the boot process. Rather, these devices are initialized within the OS. As a result, this task can be done in a matter of two seconds. In the past, the same task would need as much as 10 seconds to work in the firmware. Operating systems such as Windows 8 may benefit from fewer steps when loading the OS via UEFI. Consequently, this results in a much lower boot time [8].

Conclusion

In this article, I have succinctly covered the boot process on Linux OS. I have tried to cover the two most used approaches: BIOS and UEFI. Although lengthy, this is actually a very brief introduction to the boot process. Covering every aspect and defining every term involving the boot process would require a large book. Instead, I have tried to showcase a basic idea of how the boot process flow works.

Also, the boot process is continuously evolving. Most modern systems are working on UEFI platforms with backward support for legacy BIOS. Moreover, current UEFI-compliant firmware is quite similar to a mini operating system. In contrast, the legacy BIOS firmware has many limited functionalities.