3 How does a processor work

Common processor Architecture

• Harvard

  • optimized for speed
  • program and data memories are contained in separate machines that can be accessed simultaneously
  • typically deployed on simple processors

• Von-neumann

  • flexible design in which program and data share a common house
  • not as efficient
  • enables features not available in Harvard machines
  • used in complex and most general purpose
  • requires higher clock freq
  • 

Integrated circuit cost

• Cost per die

$\frac{\text{cost per wafer}}{\text{dies per wafer* yeild}}$

CPU performance

• CPU exc time = cpu clock cycle x clock cycle time

• CPU exec time = $\frac{\text{cpu clock cycles }}{clockrate}$

  • performance improved by

    • reducing number of clock cycles
    • increasing clock rate
    • hardware designer must often trade off clock rate against cycle count

• Clock cycels = instruction count x cycles per instruction (CPI)

• CPU time = Instruction count x CPI x Clock cycle time

$\frac{\text{instruction count x CPI}}{\text{Clock Rate}}$

• instruction counts

  • determined by
    • program
    • ISA
    • compiler

• average cycles per instruction (CPI)

  • determined by CPU hardware
  • diff instructions have different CPI
    • that’s why we are using the average value

• Big picture