Linux is a very open, customizable, and complex operating system. It’s also a great starting point for learning how computers operate because it gives us insight into the processes involved. For example, the boot process has three steps, and the final two are pretty complicated steps. After performing and ensuring the system passes a Power On Self Test (post test) it immediately attempts to identify your bootloader so it can boot your operating system for you.
Nowadays your options for Linux bootloaders basically come down to GRUB Legacy and GRUB2, but there are other options for bootloaders. GRUB provided a very simple GUI (graphical user interface) for configuring how your operating systems booted. Without getting too deep into the weeds, GRUB2 is just more flexible and customizable. They’ll both attempt to communicate with your firmware which will be either BIOS (Basic Input/Output System) or UEFI (Unified Extensible Firmware Interface). UEFI replaced BIOS as a standard in the late 90s/early 00s because it is easier to work with and more secure.
The final step is for the system to load the kernel and background software required for the operating system to run. A kernel is the primary interface between the operating system and the hardware. Other necessary software can be X11, which provides your GUI (last time I knew) on Linux. A working replacement for X11 is called Wayland. There are other processes that need to be run in the background so your keyboard, mouse, and anything else you need will be operable. When this is done by the system automatically it can feel like magic, and that is the goal of a good boot up.
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