The Power Wall

• This is section 1.7
• With the current technology
  • Energy is consumed when transistors switch
    • This is the Capacitive Load
    • It is per transistor
    • Based on the fanout or the number of transistors to which the output of a transistor is connected
    • And on the technology.
  • The power needed is given as

    
    Power ∝ Capacitive Load x Voltage 2 x Frequency Switched
        

  • Frequency switched is (related to) the clock rate
  • And voltage is the voltage needed to drive the circuit.
• So as clock speed and transistor count goes up, voltage must go down or power consumption will increase.
• The picture on page 40 demonstrates this
  • But notice, the power has not gone up with the speed and number of transistors.
  • That is because we have been able to reduce voltage.
• Unfortunately, we can't decrease voltage much (any) more with what we know.