A computer is a programmable machine. Analog computers are almost never used outside fo experimental settings. A digital computer is a programmable sequential state machine. 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.