A power-on self-test (POST)
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. This article mainly deals with personal computers, but many other embedded systems such as those in major appliances, avionics , communications, or medical equipment also have self-test routines which are automatically invoked at power-on. 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. Since a self-test might detect that the system's usual human-readable display is non-functional, an indicator lamp or a speaker may be provided to show error codes as a sequence of flashes or beeps. In addition to running tests, the POST process may also set the initial state of the device from firmware. In the case of a computer, the POST rou...