Final answer:
The BIOS searches for operating system instructions in the Master Boot Record (MBR) or GUID Partition Table (GPT) located in the first sector of the bootable drive to boot a PC.
Step-by-step explanation:
The location on a hard disk that the BIOS searches for operating system instructions in order to boot a PC is the Master Boot Record (MBR) or GUID Partition Table (GPT) depending on the disk's partitioning scheme. The BIOS initially performs a power-on self-test (POST) and then looks for the MBR or GPT on the first sector of the bootable drive, which contains the bootloader that is crucial for starting the operating system.