How a PC Starts Up

When a personal computer is switched on, it goes through a fixed sequence of steps called the boot process before it is ready to use. Power first reaches the components, then firmware on the motherboard takes control and prepares the hardware. Understanding this sequence is helpful for beginners, because many startup problems can be traced to a particular stage, such as the hardware check or the search for an operating system.

The firmware that runs first is the BIOS, stored on a chip on the motherboard. It performs a power-on self-test that checks essential parts of the system, including the processor and memory, to confirm they are working. The chipset and the configured settings determine how the hardware is initialised. If a serious fault is found at this stage, the machine may stop and signal the problem with beeps rather than continuing to start.

Once the hardware passes its checks, the BIOS looks for a bootable device in a configured order, which can include a hard drive, an optical disc or a removable boot disk. It loads a small startup program from that device, which in turn loads the operating system into memory and hands over control. A boot disk, such as a CD-ROM that can start the machine, is useful when the normal startup fails, since it lets the computer run independently of the installed system for repair or diagnosis.

Frequently asked questions

What is the boot process?

It is the sequence a computer follows from power-on, through the BIOS hardware check, to loading the operating system and becoming ready to use.

What is a boot disk?

A boot disk is a removable medium, such as a bootable CD-ROM, that can start the computer independently of the installed system, useful for repair or diagnosis.

What does the BIOS check at startup?

Through the power-on self-test it checks essential components such as the processor and memory before letting the system continue to start.