What loads first when you boot your PC?

When you boot your PC, the first component that loads is the Basic Input/Output System (BiOS) or Unified Extensible Firmware Interface (UEFI), which initializes hardware and performs the Power-On Self Test (POST). After successful POST, the BiOS/UEFI locates the boot device (such as a hard drive or SSD) based on the boot order settings. It then loads the operating system's bootloader from that device into memory, allowing the OS to start up and take control of the system.