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• Overview of main internal components of a processor and the buses that connect them to main memory

  1. Central processing unit works out what it needs to do

  2. Interacts with main memory reading and writing info

  3. Produces output in the form of visuals, sound or vibration feedback
• Control unit


  • Coordinates activities of the processor
  • Directs the flow of data between the CPU and all other devices
  • FDE cycle starts and stores the results of data back into memory
  • Sends memory read and write requests to main memory
  • Sends other command and control signals like bus requests & interrupts
• Program counter


  Holds the address of the next instruction in memory which needs to be executed
• Memory address register


  Holds the address of the memory location from which data or instruction is to be fetched or which data is to be written
• Memory data register


  Temporarily stores any data which is read from or is about to be written to main memory
• CIR

  Holds the current instruction being executed, containing an op code and an operand
• Arithmetic logic unit (ALU)


  • Performs arithmetic and logical operations on data
• Accumulator


  One of the general purpose registers that temporarily holds the results of calculations
• Address bus


  • Unidirectional, carries the memory addresses from the processor to main memory
• Data bus


  • Bi-directional, carries the binary data being transmitted around the CPU
• Control bus


  • Bi-directional, carries command and control signals to and from every other component on the CPU
• Computers use assembly code, a language with a direct one-to-one relationship with the processor architecture
• Assembly code mnemonics are short 3-4 letter codes that represent low-level processor instructions
• Decode unit


  • Looks up the binary operation code in a table to prepare the execution of an instruction
• Clock


  Generates pulses at a constant rate (clock speed) to synchronize related components
• Interrupt register


  Checked by the CPU to see if an interrupt is awaiting processing, triggering an interrupt service routine
• Cache


  Small, fast memory area locate near the CPU, providing quick access to frequently used instructions and data
• Unidirectional


  Data flows in one direction only