A boot sequence is the initial set of operations that the computer performs when it is switched on.
The bootloader typically loads the main operating system for the computer.Most computer systems can only execute code found in the memory (ROM or RAM).
Modern operating systems are stored on hard disks, or occasionally on LiveCDs, USB flash drives, or other non-volatile storage devices. When a computer is first powered on, it does not have an operating system in memory.
The computer's hardware alone cannot perform complex actions such as loading a program from disk, so an apparent paradox exists: to load the operating system into memory, one appears to need to have an operating system already loaded.
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