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.

(2001-03-30)