Computer Architecture & Von Neumann Architecture

• CPU consist:

  • Control Unit (CU)
  • Arithmetic Logic Unit (ALU)
  • Registers
  • Bus
• Control Unit: read instruction from memory
• Arithmetic Logic Unit: performs mathematical and logical operations
• Registers: execute data/instructions
• Bus: pathways that move data/instructions
• Current Instruction Registers (CIR): stores the current instruction being decoded and executed
• Accumulator (ACC): used to carrying out ALU calculations, stores data temporarily during calculations
• Memory Address Register (MAR): stores the address of the memory location currently being read from or written to
• Memory Data Register (MDR): stores data which had just been read from memory or data which is about to be written to memory
• Program Counter (PC): stores the address where the next instructions to be read can be found
• Address Bus: unidirectional - carries address only between memory and CPU
• Data Bus: bidirectional - carries data between memory and CPU
• Control Bus: bidirectional - carries signals from control unit to all other computer components
• System clock: the clock cycle to ensure synchronisation in all computer operations
• The purpose and use of an instruction set for a CPU

  • An instruction set is a list of all the commands
  • Can be processed by a CPU and the commands are machine code
• The Fetch-Execute Cycle:

  • PC contains the address of the next instruction to be fetched
  • This address is copied to the MAR via the address bus
  • The instruction of the address is copied into the MDR temporarily
  • The instruction in the MDR is then placed in the CIR
  • The value in the PC is incremented by 1, pointing to the next instruction to be fetched
  • The instruction is finally decoded and then executed