The borders between those three terms are highly ambigious, non-contiguous, and erratically shifting. The processor is the part of the computer that actually does the computations. Some computers have more than one processor. This is called multi-processing . It also performs shift and rotate operations and other specialized operations.
Control units fetch and decode machine instructions.
Control units may also control some external devices. An internal bus is a bus inside the processor, moving data, addresses, instructions, and other information between registers and other internal components or units. For more information, see buses . RAM is Random Access Memory, and is the basic kind of internal memory. Most modern RAM is made from integrated circuits.