Register also sometimes known as the accumulator, is a temporary storage position where data coming from RAM heading to the processor for execution and data coming from the processor after processing is held. Thus a register is a local storage area within the processor that is used to hold data that is being worked on by the processor.
Internal Registers (Internal Data Bus)
This is the bus connecting the internal components of the processor to the motherboard. The size of the internal registers indicates how much information the processor can operate on at one time and how it moves data around internally within the chip. This is sometimes also referred to as the internal data bus. A register is a holding cell within the processor; for instance, the processor can add numbers in two different registers, storing the result in a third register. The register size determines the size of data on which the processor can operate.