Which of the parts of a computer actually executes the program instructions?

The Central Processing Unit (CPU) is the part of a computer that actually executes the program instructions. Here's a step-by-step breakdown of how it works:

1. Fetch: The CPU fetches the instruction from the computer's memory. This is done by the control unit, which is a part of the CPU. It reads the data that is stored at the address in the memory that the PC (program counter) is pointing to.

2. Decode: Once the instruction is fetched, it needs to be decoded or translated into commands that the computer can understand. The control unit also does this.

3. Execute: After the instruction is decoded, it's time for the ALU (Arithmetic Logic Unit), another part of the CPU, to execute the instruction. This could involve doing some sort of calculation or making a decision (like comparing two numbers).

4. Store: The final step is to store the result of the instruction. This could be in the CPU's own registers (if it's a temporary result), or back in the computer's memory (if it's a final result).

So, in summary, the CPU is the part of the computer that executes program instructions.