A processor is a functional unit that interprets and carries out instructions． Every processor comes with a unique set of operations such as ADD， STORE， or LOAD that represent the processor's instruction set． Computer designers are fond of calling their computers machines， so the instruction set is sometimes referred to as machine instructions and the binary language in which they are written is called machine language！
An instruction is made up of operations that specify the function to be performed and operands that represent the data to be operated on. For example, if an instruction is to perform the operation of adding two numbers, it must know (l)what the two numbers are and (2)where the two numbers are. When the numbers are stored in the computer's memory, they have an address to indicate where they are, so if an operand refers to data in the computer's memory it is called an address. The processor's job is to retrieve instructions and operands from memory and to perform each operation. Having done that, it signals memory to send it the next instruction.
A processor is composed of two functional units—a control unit and an arithmetic/logic unit, and a set of special workspaces called registers. The control unit is the functional unit that is responsible for supervising the operation of the entire computer system. The control unit fetches instructions from memory and determines their type or decodes them. It then breaks each instruction into a series of simple small steps or actions. By doing this, it controls the step-by-step operation of the entire computer system. The arithmetic /logic unit (ALU)is the functional unit that provides the computer with logical and computational capabilities. Data are brought into the ALU by the control unit, and the ALU performs whatever arithmetic or logic operations are required to help carry out the instruction. A register is a storage location inside the processor. Registers in the control unit are used to keep track of the overall status of the program that is running. Control unit registers store information such as the current instruction, the location of the next instruction to be executed, and the operands of the instruction. In the ALU, registers store data items that are added, subtracted, multiplied, divided, and compared. Other registers store the results of arithmetic and logic operations.
