Power-on self-test

The POST (of English power-on self -test ) is a self-test after turning on the computer - a process that the computer at startup goes through in order to check whether the basic components of the PC are functional. Any errors are frequently first reported by characteristic beeps and after successful commissioning of the graphics card on the screen.

Expiration

The POST is performed by the BIOS. This is the first program, which executes the computer after turning.

The POST can be divided into steps. The following steps are part of each POST:

After that, the graphics card can be put into operation. The other tests are therefore usually made ​​visible on the screen:

• Review of the remaining memory - this step can be skipped in some BIOS by pressing a key
• Review of the keyboard
• Review of other peripherals, including floppy drives and hard drives

During POST, there is usually a way to call a BIOS setup program to change system settings.

Since the specific implementation of the POST of the BIOS may vary BIOS, can be added or omitted some of these points more points. Some tests, such as floppy drive or the full test of the working memory can also be turned off in the BIOS setup.

Error Messages

The BIOS reports errors that are detected during POST, directly. If the graphics system already tested and in operation, the message is on the screen; otherwise, the message is often carried out by acoustic or visual signals through the system speakers or the flashing instructions for any status display. The signals in different duration and frequency indicate the type of error. Their importance depends on the BIOS manufacturer.

Output using POST Card

A detailed diagnosis is possible using a POST card, a plug-in card, which indicates the current status of the POST with the help of light-emitting diodes or a digital display. If the display remains at boot standing on a value, you can determine the problem with the help of a mainboard associated error code table. The values ​​were originally from 0x00h output continuously ( with errors equal in executing the first BIOS commands on the CPU) to 0xFFh (POST completed) on the I / O port 0x80h. Depending on the BIOS, and partly also the used hardware used can control the order and the meaning of displayed codes vary greatly.