What Happens When You Press the Power Button?
So when you press that power button, what exactly happens? In simple terms, the system is going to go through the boot process, a process that is overseen by the one and only BIOS. It doesn't seem like the system is going through an entire process because it all happens so fast, but within those few seconds, a lot happens. For those curious, we've outlined the basics of what happens in those few seconds between the moment you press the power button and when the operating system start menu welcomes you.
1. Power On
You press the power button and the power supply turns on. Once the system receives a "Power Good" signal from the power supply, the CPU will seek instructions from the BIOS about initializing the system and the BIOS will start interfacing with the hardware. The system ROM BIOS will then start feeding the system instructions.
2. Power-On Self Test (POST)
The BIOS will first instruct the system to go through a Power-On Self Test, also known as POST. This step is will allow the system to identify any potential hardware failures within the system, check to see if everything is functioning properly and run tests. During POST, various parts of the system are checked including:
- Hard drives
The CPU must also successfully initialize to start the system. If POST returns with errors, the boot process will stop and beep codes will help indicate what problems are affecting the boot process.
3. OS Boot
Once the CPU has successfully initialized, the BIOS will seek the operating system to boot to and load. The system will look through the boot device list and select the operating system to load. At this point, the BIOS is getting ready to hand off the rest of the process off to the operating system.
4. OS Loads and Takes Control
Once the OS completes loading, the OS will then take the reins and the OS will then execute startup applications. This means your computer is now is ready to use and the boot process is complete.
All that happens in just a span of seconds. It's quite fascinating to see how technology has allowed the computer boot process to become so fast, that your system is up and running in just a few seconds!