Double boot (also known as cold double boot, double cold boot, double POST, power-on auto reboot, or fake boot) is a feature of the

BIOS In computing, BIOS (, ; Basic Input/Output System, also known as the System BIOS, ROM BIOS, BIOS ROM or PC BIOS) is firmware used to provide runtime services for operating systems and programs and to perform hardware initialization during the b ...

, and may occur after changes to the BIOS' settings or the system's configuration, or a

power failure A power outage (also called a powercut, a power out, a power failure, a power blackout, a power loss, or a blackout) is the loss of the electrical power network supply to an end user. There are many causes of power failures in an electrici ...

while the system was in one of certain

sleep mode Sleep mode (or suspend to RAM) is a low power mode for electronic devices such as computers, televisions, and remote controlled devices. These modes save significantly on electrical consumption compared to leaving a device fully on and, upon resu ...

s. Changing some parameters in the BIOS will cause this issue, even for items as simple as initializing the current

CPU A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuitry that executes instructions comprising a computer program. The CPU performs basic arithmetic, logic, controlling, and ...

and memory

clock A clock or a timepiece is a device used to measure and indicate time. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month and the ...

s. At such times, a

reboot In computing, rebooting is the process by which a running computer system is restarted, either intentionally or unintentionally. Reboots can be either a cold reboot (alternatively known as a hard reboot) in which the power to the system is phys ...

will be required. If the

computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These prog ...

did not have any power and had just been plugged in, the same parameters would need to be implemented again, and since these parameters require a reboot, the computer will do a quick reset to implement the parameters that are set in the BIOS. Even after the computer is turned off, these parameters will not need to be re-entered for as long as the

power supply A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As ...

is still receiving power. In a double boot, the PC will power on for about two seconds, off for about a second, turn back on, display the POST screen, and then continue to boot up normally.

References

BIOS {{computer-stub