Booting up

Booting up refers to the process that a computer or a computer system undergoes from the moment power is applied to the system to the point where it is ready for use by the user. This process involves a series of steps executed by the computer's hardware and software, culminating in the loading of the operating system (OS). The term "booting" is short for "bootstrapping," which metaphorically refers to the impossible task of "pulling oneself up by one's bootstraps" and highlights the paradox of a computer needing to run code to load the operating system but needing the operating system loaded to run code.

Process

The booting process can be divided into several key stages:

Power-On Self-Test (POST)

When the computer is first powered on, the Basic Input/Output System (BIOS) or Unified Extensible Firmware Interface (UEFI) firmware performs the POST. This is a preliminary test to ensure that the essential hardware components like RAM, processor, and disk drives are functioning correctly.

Bootloader

After the POST, the BIOS/UEFI identifies and executes a bootloader program. The bootloader's primary function is to load the operating system from the computer's storage devices into RAM. In systems with multiple operating systems, the bootloader allows the user to select which OS to boot.

Operating System Loading

The bootloader then loads the kernel of the operating system into memory. The kernel initializes the system's hardware and software environment, mounts the root filesystem, and starts system processes. This stage culminates in the user being presented with a login screen or desktop environment, marking the system as ready for use.

Types of Booting

There are two main types of booting:

• Cold Booting: Also known as hard booting, this involves starting the computer from a completely powered-off state.
• Warm Booting: Also known as soft booting, this involves restarting the computer without turning off the power, usually by pressing the reset button or using the operating system's restart function.

Booting Devices

The device from which a computer boots is typically a hard disk drive (HDD), solid-state drive (SSD), optical disc, or USB drive. The choice of boot device is configured in the system's BIOS/UEFI settings.

Booting Problems

Common issues during the booting process include hardware failures, corrupted bootloaders, missing system files, or problems with the operating system itself. Such problems can lead to boot failure, where the system does not reach a usable state and may require troubleshooting or repair.