All computers, regardless of size, classification or operating system, have a bootup process that gets executed at power on. The term "boot" comes from the old saying about "pulling yourself up by your bootstraps," and originally was referred to as the "bootstrap" process. Once this process completes, it turns over control to the installed OS, having ensured that all is well with the computer.
Of course, the first step of the process is the power-on step, which is typically initiated by the user. More recent developments allow for a "wake on LAN" setting, which facilitates a power-up across the network, so no physical user presence or action is required. As power is applied, the CPU executes code in read-only memory (ROM), located on the motherboard.
After executing the ROM routines, the system executes a Power-On Self Test (POST) routine, which ensures all hardware is operational and ready to go. This includes checking memory and hard drives. Once the POST is finished, the system looks for the first device in the boot order list.
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The system looks for an active device in the boot device list, starting at the top. When it finds an available device, it loads the Basic Input/Output System (BIOS) from the device. The BIOS provides information on basic communications with peripheral devices, and communications on the motherboard itself.
Load the Operating System
After ensuring the hardware is functional and loading the BIOS, the computer proceeds to load the operating system into memory. The specific OS is not relevant, as long as its drivers can talk to the hardware on the machine. Any OS-specific configuration routines are also executed as part of loading the OS.
Transfer Control to the OS
Once the OS is loaded, the boot process turns control over to it, and any OS-specific startup applications are executed by the OS. These startup routines vary from one user to another, based on the user's preferences and desired configuration. When the startup applications complete, your computer is ready to use.