Power-on self-test
<hardware> (POST) A sequence of diagnostic tests that are run automatically by a device when the power is turned on.
In a
personal computer a typical POST sequence does the following:
- checks that the
system board is working
- checks that the
memory is working
- compares the current system configuration with that recorded by the PC's configuration program to see if anything has been added or removed or broken
- starts the video operation
- checks that the
diskette drive,
hard disk drive,
CD-ROM drive, and any other drives that may be installed are working.
When POST is finished, typically it will
beep, and then let your
operating system start to
boot.
If POST finds an error, it may beep more than once (or possibly not at all if it is your PC speaker that is broken) and display a POST error message.
These messages are often nothing more than a single ominous number.
Some common numbers and their meanings are:
161 Dead battery (get a new battery for the system board)
162 Configuration changed (you added some memory or a new card to the PC)
301 Keyboard error (take the book off the corner of the keyboard)
Because a successful POST indicates that the system is restored to known state, turning the power off and on is a standard way to reset a system whose software has
hung. Compare
120 reset,
Big Red Switch,
power cycle.
