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Power-on self-test

(also POST)

Power-on self-test definition

The power-on self-test (POST) is an automated check a computer does when powered on to make sure all hardware components are working properly. POST checks if the CPU, RAM, and storage devices are all functioning as they should and shows an error if they’re not. This automatic test helps detect hardware issues early and makes sure your computer is good to go (from the hardware perspective).

How does POST work?

  • When you turn on your computer, electricity flows through it, and the hardware components receive power.
  • The computer's central processing unit (CPU) starts running basic instructions from a special chip called the BIOS (Basic Input/Output System), which is responsible for hardware management.
  • The BIOS kicks off the POST process. It sends signals to different hardware components, telling them to start their self-checks.
  • Each hardware component (e.g., CPU, RAM, or graphics card) runs a quick self-check to check all is working as it should.
  • If any component fails its self-check, it sends an error signal back to the BIOS.
  • If there are errors, the BIOS shows error messages to help technicians or users understand which hardware component is causing trouble.
  • If all hardware components pass their self-checks without errors, the BIOS reports a successful POST. You might see a message like “System Passed POST” or “No Errors Found.”
  • After a successful POST, the BIOS hands over control to the operating system loader. The operating system then loads, and your computer is ready to use.