Which component is responsible for executing program instructions within the CPU?

The component responsible for executing program instructions within the CPU is the Arithmetic Logic Unit (ALU). The ALU performs all arithmetic operations (like addition and subtraction) and logic operations (like comparisons). When a program is executed, it is the ALU that processes the specific calculations and logical decisions as dictated by the program’s instructions.

While registers play an essential role in the CPU by temporarily holding data and instructions that the ALU is currently processing, they do not execute commands themselves. The BIOS is a firmware that initializes hardware during the startup process and facilitates booting the operating system, but it does not partake in executing program instructions. RAM serves as the system's short-term memory, storing data and instructions that are actively being used but does not have the capacity to execute them. Therefore, the ALU clearly stands out as the component that carries out the actual execution of program instructions within the CPU.