The Processor and its Components

The Processor and its Components

The Processor

  • Also known as the Central Processing Unit (CPU), the processor acts as the brain of a computer.
  • It performs various functions including the processing of instructions from programs, and the input/output operations.
  • The speed of a processor is measured in Hertz (Hz). A processor that is rated at one gigahertz is capable of executing one billion cycles per second.
  • Stocks to a clock called a system clock which sends out a regular stream of electronic pulses that synchronize all computer operations.

Components of a Processor

Control Unit (CU)

  • The Control Unit (CU) manages and controls the operations of the CPU.
  • It decodes instructions and transforms them into a series of control signals which operate other parts of the computer.
  • The CU communicates with both the Arithmetic Logic Unit (ALU) and memory.

Arithmetic Logic Unit (ALU)

  • The Arithmetic Logic Unit (ALU) performs arithmetic and logical operations on binary data.
  • It can carry out basic tasks such as addition, subtraction, multiplication, and division. For more complex calculations, it combines these basics.
  • In addition to arithmetic operations, the ALU performs bit-shifting and logical operations, including AND, OR, and NOT functions.


  • Registers are small storage locations used to quickly hold and retrieve data and instructions that are being used or processed.
  • The number and type of registers vary between CPUs, but some common types include the accumulator, data register, address register, and instruction register.
  • The Program Counter (PC) is a special register that keeps track of the location in memory where the next instruction is to be fetched from.
  • The Memory Data Register (MDR) holds the data being transferred to or from memory.
  • The Memory Address Register (MAR) holds the address in memory of the next instruction or data.


  • A bus is a system that transfers data between components inside a computer, or between computers.
  • The data bus carries data among the processor, memory, and I/O devices.
  • The address bus carries addresses for memory locations.
  • The control bus carries command and control signals to and from every other component of the computer.

Clock and Cache

  • The clock sets the pace for the processor operations, with each tick representing one clock cycle.
  • The processor’s speed is determined by its clock speed, measured in gigahertz (GHz).
  • The cache is a small, high-speed memory located close to or inside the processor, used to store frequently or recently used information.

Execution of Instructions

  • The cycle of fetching, decoding, executing, and storing is known as the Fetch-Decode-Execute (FDE) cycle or the instruction cycle.
  • Fetch: The next instruction is fetched from the memory address that is currently stored in the PC, and stored in the instruction register. Once the fetch is complete, the PC is updated to point to the next instruction.
  • Decode: The CU decodes the instruction in the IR and prepares the system to execute the instruction.
  • Execute: The ALU executes the instruction.
  • Store (Write back): The results from the ALU are saved to the appropriate register or memory location.