Hard reboot

In computing, rebooting is the process by which a running computer system is restarted, either intentionally or unintentionally. Reboots can be either cold (alternatively known as hard) where the power to the system is physically turned off and back on again, causing an initial boot of the machine, or warm (alternatively known as soft) where the system restarts without the need to interrupt the power. The term restart is used to refer to a reboot when the operating system closes all programs and finalizes all pending input and output operations before initiating a soft reboot.

Early electronic computers (like the 1401) had no operating system and little internal memory. The input was often a stack of punch cards. The computer was initiated by pressing a start button that performed a single command, read a card. This first card then instructed the machine to read more cards that eventually loaded a user program. This process was likened to an old saying, "picking yourself up by the bootstraps", referring to a horseman who lifts himself off the ground by pulling on the straps of his boots. This set of initiating punch cards was called "bootstrap cards". Thus a cold start was called booting the computer up. If the computer crashed, it was rebooted. The boot reference carried over to all subsequent types of computers. For more, see Bootstrapping.

Technical sources describe two contrasting forms of reboot known as cold reboot (also cold boot, hard reboot or hard boot) and warm reboot (also warm boot, soft reboot or soft boot) although the definition of these forms slightly vary between sources.

According to Jones, Landes, Tittel (2002), Cooper (2002), Tulloch (2002) and Soper (2004), on IBM PC compatible platform, a cold boot is a boot process in which the computer starts from a powerless state. All except Tulloch (2002) also mention that in cold boot, system performs a power-on self-test (POST). In addition to the power switch, Cooper (2002) and Soper (2004) also state that reset button may commence a cold reboot. Jones, Landes, Tittel (2002) contradicts this assertion and states that a reset button may commence either a cold or warm reboot, depending on the system. Microsoft Support article 102228 also confers that although the reset button is designed to perform a cold reboot, it may not disconnect the power to the motherboard – a state that does not correspond to the cold boot definition given above. According to Jones, Landes, Tittel (2002), both the operating system and third-party software can initiate a cold boot; the restart command in Windows 9x initiates a cold reboot, unless Shift key is held.

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