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A boot sequence is the series of essential steps a computer performs to start up, including initializing hardware, running self-tests, and loading the operating system into memory, making the system ready for user interaction. Controlled by the BIOS or UEFI, this process begins with power-on and involves a Power-On Self-Test (POST) to check components, then locating and loading the operating system from a designated boot device like a hard drive or SSD.

Key Steps in the Boot Sequence

Power On & Initialize Hardware: When a computer is powered on, the BIOS or UEFI firmware provides initial instructions to the Central Processing Unit (CPU).

Power-On Self-Test (POST): The BIOS/UEFI performs a POST to verify that essential hardware components, such as the CPU, memory (RAM), and storage devices, are functioning correctly.

Find the Boot Device: The system then searches for a bootable device, which is the storage medium containing the operating system. The order in which it checks these devices is the "boot order" or "boot sequence".

Load the Operating System: Once a bootable device is found, the system loads the operating system's bootloader into the computer's main memory.

System Configuration and User Authentication: The operating system then takes over, loading necessary drivers and system utilities, and prepares for user authentication if a password is set, making the computer ready for use.