CPU Power On Self Test (POST)

EVERY PART of a PC must be functioning to truly process data into information! When you turn on your computer the boot process performs the "POST" test after the ROM BIOS is loaded into memory:

The "POST" tests are made to determine if all its parts are in working order.

The POST process consists of checking each of the following parts of the computer:

  1. CPU
  2. Power System
  3. Speaker
  4. Disk Drives
  5. Monitor
  6. Keyboard
  7. Memory
  8. etc.
The POST process is responsible for the "beeps" you hear when booting, and also the messages the error messages such as:

"keyboard error press to continue for setup"

ROM BIOS program starts the POST tests using permanent records stored on chips and the steps are:

  1. The CPU to checks itself and the POST programs.
  2. Sends signals over the system bus to all devices to make sure they are working.
  3. The "kernal" and the timing are checked.
  4. Memory on the display adapter is tested, and the adapter's BIOS code is made a part of the system's BIOS and memory configuration.
  5. RAM is tested to make sure all RAM chips are working properly.
  6. Checks to see the keyboard is working properly.
  7. Checks to see if the Disk Drives are working.
  8. Compares the results of the POST tests against CMOS to see if what it found matches the CMOS setup record.
  9. Finds devices that have their own BIOS and includes it in the system BIOS.
  10. Newer systems may run a "Plug and Play (PnP) operation.

If everything in the POST worked, the PC is now going to load the operating system.

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Basic PC Components