Sometimes, a processor must handle more than a single bit of data at a time. For example, it is more efficient for a processor to work with a group of bits when transferring data to and from memory. Also, storing numbers and codes requires a grouping of bits. A group of bits handled simultaneously is called a byte. More accurately, a byte is the smallest group of bits that can be handled by the processor at one time. Although byte size is normally eight bits, this size can vary depending on the specific controller.