The BIOS checks the integrity of the RAM, GPU, and other essential hardware.

Converts the PSU’s 12V rail into the precise, low-voltage "VCORE" needed by the processor.

: The SIO chip informs the Platform Controller Hub (PCH) or chipset to start the boot process.

Pressing the power button sends a signal to the SIO, which then communicates with the South Bridge (PCH). Wake-Up Signals: The South Bridge responds with

: The SIO chip pulls the PSON# line low, telling the PSU to turn on all main voltage rails (+12V, +5V, +3.3V).