Which part of the CPU is responsible for executing instructions

Question

I was reading about the machine cycle. Everything was clear until I started with the execution of instructions. I know how an ALU and a CU work. I'm also aware of the process of fetching and decoding. But, I'm a little bit confused about the part that is responsible for executing instructions in a CPU.

Note: I've searched for an answer before asking. However, nothing was helpful enough.

Answer 1

• All the parts of the CPU are executing instructions at some point of time or the other.
• The part(s) that is/are executing an instruction at a given time depends on the instruction being executed.
• For example, in an add instruction, the ALU performs addition in the execute stage of the instruction cycle.
• Through a process called pipelining, more than one instruction can be executed on a CPU. For example, data can be fetched in the Load stage while addition is being performed in the execute stage in the same cycle.
• Optimizing compilers try to keep the whole CPU busy by reordering instructions such that all the parts of the CPU are busy most of the time.