In computer architecture, a processor register is a small amount of storage available on the CPU whose contents can be accessed more quickly than storage available elsewhere.Processor registers are at the top of the memory hierarchy, and provide the fastest way for a CPU to access data. The term is often used to refer only to the group of registers that are directly encoded as part of an instruction, as defined by the instruction set. The General Purpose registers can store both data and addresses, i.e., they are combined Data/Address registers.. The Data register can store data. The Address register can store data. The Condition Codes register hold truth values often used to determine whether some instruction should or should not be executed. .