Os boot process
To work on operating system it is mandatory to understand its loading process. so here we will cover os booting in general.
Also we will see different types of booting and dual booting.
So first understand ,what is booting..
Booting
It is the process of starting or initializing the computer’s software components, primarily the operating system itself, to make the computer ready for user interaction.
There are 2 types of booting
Warm booting/Soft booting
Warm booting refers to the process of restarting a computer without turning off its power entirely. It’s sometimes called a “soft reboot” because the computer doesn’t go through the complete power-on sequence.
In a warm boot, the computer’s power remains on while you initiate the restart (e.g., using a software command like “Restart” from the operating system or pressing a specific key combination). The computer doesn’t go through the POST (Power-On Self-Test) phase and BIOS/UEFI initialization again.
Cold booting/ Hard booting
Cold booting refers to the process of starting a computer from a completely powered-off or “cold” state.
In a cold boot, the computer’s power is initially turned off. When you press the power button, the computer goes through the entire boot process, including hardware initialization, BIOS/UEFI startup, and loading the operating system.
Steps of Booting in general of OS.
1. Power On and CPU will move to BIOS (Basic Input/Output System) in ROM
The first step involves turning on the power. It powers the essential parts, including the processor and BIOS in ROM
BIOS test runs a preliminary examination of the computer’s main memory, disk drives, input/output devices, etc. Moreover, the system emits a beep sound in case of any errors. This is called POST (POWER ON SELF TEST) which is executed in BIOS.
**BIOS and UEFI is a firmware .
2. (BIOS will load MBR to RAM) and (UEFI will load ESP to RAM).
Depending on whether the system is using the traditional BIOS or UEFI, one of the following processes occurs:
MBR (BIOS): If the system is using the BIOS, it loads the Master Boot Record (MBR) from the selected boot device’s first sector (typically the first 512 bytes). The MBR contains a small program that points to the location of the bootloader for the installed OS.
UEFI Firmware: If the system is using UEFI, it loads the EFI System Partition (ESP), which contains EFI boot loaders. UEFI firmware knows the location of the bootloader for each installed OS on the ESP and passes control to the appropriate bootloader.
3. Bootloader is loaded in RAM by MRP or ESP
The bootloader (e.g., GRUB for Linux, NTLDR for Windows) takes control. It provides a menu, if configured, allowing the user to select the OS to boot if multiple OSes are installed. The bootloader’s primary job is to load the kernel (the core of the operating system) into memory.
4. Bootloader will load OS to RAM
Once the bootloader has loaded the OS, the kernel takes over. It initializes the essential parts of the operating system, including device drivers, memory management, and file systems.
This is the full process of Booting…
Dual Booting
Dual booting is a setup in which a computer has two different operating systems installed on the same storage device (such as a hard drive or SSD), and the user can choose which operating system to boot into when starting the computer. This allows you to run two or more operating systems on a single computer, each in its own separate partition or space on the storage device.
Once it has been loaded, one of the operating systems on the disc can be booted.
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