Power-on self-test

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A power-on self-test (POST) is a process performed by firmware or software routines immediately after a computer or other digital electronic device is powered on.^[1]

POST processes may set the initial state of the device from firmware and detect if any hardware components are non-functional. The results of the POST may be displayed on a panel that is part of the device, output to an external device, or stored for future retrieval by a diagnostic tool. In some computers, an indicator lamp or a speaker may be provided to show error codes as a sequence of flashes or beeps in the event that a computer display malfunctions.

POST routines are part of a computer's pre-boot sequence. If they complete successfully, the bootstrap loader code is invoked to load an operating system.

In IBM PC compatible computers, the main duties of POST are handled by the BIOS or UEFI.