EE466_L05 - Wednesday Sept. 2, 2009 Based in part on slides...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Wednesday Sept. 2, 2009 Based in part on slides from Hennessy & Patterson AQA - 4 th Edition Technology Trends + Quantitative Comparisons b Technology Trends: We need to be able to anticipate and exploit advances in technology so look at history b Careful, quantitative comparisons: 1. Define and quantify power 2. Define and quantify dependability 3. Define and quantify and summarize relative performance 4. Define and quantify relative cost Last time Wednesday Sept. 2, 2009 Based in part on slides from Hennessy & Patterson AQA - 4 th Edition Define and quantify power b For CMOS chips, traditional dominant energy consumption has been in switching transistors, called dynamic power - power dissipated in switching b For a clocked flip-flop that toggles once per cycle: b In this era of mobile devices, energy turns out to be a better metric (battery life is of some importance) P o w e r d y n a m i c = C a p a c i t i v e L o a d V o l t a g e 2 F r e q u e n c y S w i t c h e d E n e r g y d y n a m i c = C a p a c i t i v e L o a d V o l t a g e 2 Wednesday Sept. 2, 2009 Based in part on slides from Hennessy & Patterson AQA - 4 th Edition What does this mean? b For a fixed task, slowing clock rate (frequency switched) reduces power, but not energy b Capacitive load is a function of number of transistors connected to output and technology, which determines capacitance of wires and transistors b Dropping voltage helps both, so went from 5V to 1V b To save energy & dynamic power, most CPUs now turn off clock of inactive modules (e.g. Fl. Pt. Unit) P o w e r d y n a m i c = C a p a c i t i v e L o a d V o l t a g e 2 F r e q u e n c y S w i t c h e d E n e r g y d y n a m i c = C a p a c i t i v e L o a d V o l t a g e 2 Wednesday Sept. 2, 2009 Based in part on slides from Hennessy & Patterson AQA - 4 th Edition Example of quantifying power b Suppose 15% that a reduction in voltage results in a 15% reduction in frequency. What is impact on dynamic power? (example from the text) Power dynamic = Capacitive Load Voltage 2 FrequencySwitched NewPower = Capacitive Load (.85 Voltage 2 ) (.85 FrequencySwitched) = (.85) 3 * OldPower dynamic 0.6 * OldPower dynamic Wednesday Sept. 2, 2009 Based in part on slides from Hennessy & Patterson AQA - 4 th Edition Define and quantity power (part 2) b Because leakage current flows even when a transistor is off, now static power is important too b Leakage current increases in processors with smaller transistor sizes b Increasing the number of transistors increases power consumed even if they are turned off b In 2006, goal for leakage was 25% of total power consumption; high performance designs were at 40% b In very low power systems even gate voltage to inactive modules is minimized to control loss due to leakage b In 2007, high speed 65 nm processes lost as much as half their power to leakage b Many in industry (in June 2007) believed that with 45 nm, as much as 60%...
View Full Document

This note was uploaded on 10/11/2009 for the course EE 466 taught by Professor Conry during the Fall '09 term at Clarkson University .

Page1 / 27

EE466_L05 - Wednesday Sept. 2, 2009 Based in part on slides...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online