UC Regents Spring 2011 © UCBEECS 150 L28: Power and Energy2011-4-28John Wawrzynektoday’s lecturer: John LazzaroCS 150 Digital DesignLecture 28 – Power and Energywww-inst.eecs.berkeley.edu/~cs150/TAs: Michael Eastham and Austin Doupnik 1UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyEnergy and PerformanceSad fact: Computers turn electrical energy into heat. Computation is a byproduct.Air or water carries heat away, or chip melts.2UC Regents Spring 2011 © UCBEECS 150 L28: Power and Energy+1V-1 Ohm Resistor1A0.24 Calories per SecondHeats 1 gram of water 0.24 degree CThis is how electric tea pots work ...1 Joule of Heat Energy per Second1 Watt20 W rating: Maximum power the package is able to transfer to the air. Exceed rating and resistor burns.3UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyCooling an iPod nano ...Like resistor on last slide, iPod relies on passive transfer of heat from case to the air.Why? Users don’t want fans in their pocket ... To stay “cool to the touch” via passive cooling, power budget of 5 W.If iPod nano used 5W all the time, its battery would last 15 minutes ...4UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyPowering an iPod nano (2005 edition)Battery has 1.2 W-hour rating: Can supply 1.2 W of power for 1 hour.1.2 W / 5 W = 15 minutes.Real specs for iPod nano : 14 hours for music, 4 hours for slide shows.85 mW for music.300 mW for slides.More W-hours require bigger battery and thus bigger “form factor” -- it wouldn’t be “nano” anymore :-).5UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyFinding the (2005) iPod nano CPU ...Two 80 MHz CPUs. One CPU used for audio, one for slides.Low-power ARM roughly 1mW per MHz ... variable clock, sleep modes.85 mW system power realistic ...A close relative ...6UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyiPod nano 200514 hours batterylife(audio playback)Year-to-year: continuous improvementsiPod nano 200624 hours batterylife(audio playback)What changed inside ?Source: ifixit.com7UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergySource: ifixit.com8UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergySource: ifixit.com9UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyiPod nano 2005 - a C-shaped PC board, with a battery in the “C” opening.iPod nano 2006 -battery lies on top of PC board.Source: ifixit.com10UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyHow? Small IC packages, fewer partsiPod nano 2006 iPod nano 2005 Source: arstechnica.com11UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyAluminum permits thinner case ...Source: ilounge.com12UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyiPod nano 200514 hours batterylife(audio playback)Year-to-year: continuous improvementsiPod nano 200624 hours batterylife(audio playback)What’s happened since ?Source: ifixit.com1.2 W-hour battery. 13UC Regents Spring 2011 © UCBEECS 150 L28: Power and Energy0.74 ouncesSources: iFixit, Apple0.39 W Hr2010 Nano: “up to” 24 hours audio playback2010 Nano2010 Shuffle: “up to” 15 hours audio playback0.44 ounces0.19 W Hr2010 Shufflenearly the same depth14UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyNotebooks ... now most of the PC market.Performance: Must be “close enough” to desktop performance ... most people no longer use a desktop (including me!)Heat: No longer “laptops” -- top may get “warm”, bottom “hot”. Quiet fans OK.Size and Weight. Ideal: paper notebook.1 in8.9 in12.8 in2006 Apple MacBook -- 5.2 lbs15UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyBattery: Set by size and weight limits ...Almost full 1 inch depth. Width and height set by available space, weight.Battery rating: 55 W-hour.At 2.3 GHz, Intel Core Duo CPU consumes 31 W running a heavy load - under 2 hours battery life! And, just for CPU!At 1 GHz, CPU consumes 13 Watts. “Energy saver” option uses this mode ...46x more energy than iPod nano battery. And iPod lets you listen to music for 14 hours!16UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyMacBook Air ... fits in a manila envelope!17UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyNon-removable, “form-fit” battery ...18UC Regents Spring 2011 © UCBEECS 150 L28: Power and Energy55 W-hour battery stores the energy of 1/2 a stick of dynamite.If battery short-circuits, catastrophe is possible ...19UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyLithium battery density and mass ...Source: Machine Design magazineLiterThus the interest in fuel cells for portable electronics ...20UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyThe CPU is only part of power budget!T.J. Watson Research Center© 2004, 2005 IBM Corporation6 Pradip Bose| Hot Chips 2005 Tutorial August 14, 2005Current Generation Laptop Power Pie15%4%5%1%8%26%1%3%8%29%CPU HDDPower Supply WirelessLCD LCD BacklightOptical Drive MemoryGraphics Rest of the system52%3%3%1%4%13%1%4%4%15%Idle PowerMax Power Workload(IBM Thinkpad R40)Data courtesy Mahesri et al., U of Illinois, 20042004-era notebook running a full workload.“Amdahl’s Law for Power”If our CPU took no power at all to run, that would only double battery life!T.J. Watson Research Center© 2004, 2005 IBM Corporation6 Pradip Bose| Hot Chips 2005 Tutorial August 14, 2005Current Generation Laptop Power Pie15%4%5%1%8%26%1%3%8%29%CPU HDDPower Supply WirelessLCD LCD BacklightOptical Drive MemoryGraphics Rest of the system52%3%3%1%4%13%1%4%4%15%Idle PowerMax Power Workload(IBM Thinkpad R40)Data courtesy Mahesri et al., U of Illinois, 2004CPULCD Backlight“other”LCDGPU21UC Regents Spring 2011 © UCBEECS 150 L28: Power and Energy22UC Regents Spring 2011 © UCBEECS 150 L28: Power and Energy23UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyServers: Total Cost of Ownership (TCO)Rack Stats•Weight: 1500 Lbs•Power: 98 Amps•Fans: 340 (2”) + 2 (8”)•Wire: 0.25 miles•Assembly and wiring time: 60 man-hoursMachine rooms are expensive. Removing heat dictates how many servers to put in a machine room.Electric bill adds up! Powering the servers + powering the air conditioners is a big part of TCO.Reliability: running computers hot makes them fail more often.24UC Regents Spring 2011 © UCBEECS 150 L28: Power and EnergyProcessors and Energy25UC Regents Spring 2011 © UCBEECS 150 L28: Power and Energy Switching
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