1. Practical and OS-Driven Power Management
Chris Ragsdale

2. Intro Data is stored as ones and zeros…
What does this actually look like?
How exactly does electricity power computers?

3. Layout Electricity Fundamentals Relating to Computers
Inside the CPU
Inside Memory
What does the Power Supply do?
Primary Power Consumers in Computers
CPU, Memory, HDD, Wifi transmitter/receiver, Display/GPU
Power Management
I/O States - Windows and OS X
OS power management techniques for Memory, HDD and Wifi receiver

4. Fundamentals
CPU
Memory
Power Supply

5. Fundamentals - The CPU

6. Fundamentals - Memory

7. Fundamentals - Power Supply

8. Primary Power Consumers
CPU
Memory
HDD
Wireless Transmitter / Receiver
Display / GPU

9. Primary Power Consumers - CPU
Clock cycle, Voltage and Power Consumption related
Cycle and voltage directly related
Power = Voltage^2
Dynamic Voltage Frequency Scaling
Adaptive Frequency Scaling

10. Primary Power Consumers - Memory
Power floor
Capacitors constantly leaking, must be refilled
Low power effects overall system efficiency

11. Primary Power Consumers - HDD

12. Primary Power Consumers - Wifi transmitter/receiver

13. Primary Power Consumers - Display/GPU

14. Power Management I/O Device States Examples Windows OS X Memory HDD
Wifi

15. Power Management - I/O States
Similar to Process States
Allow OS to utilize Dynamic Power Switching (DPS)
Sleep, Hibernate

16. I/O States - Windows States: D0, D1, D2, D3
0 = fully on, 1 = less power, 2 = even less power, 3 = minimum power <-> off
Each state tracks device data
Power Consumption
Device Context
Driver Behavior
Restore Time
Wake-Up Capability

17. I/O States - OS X States: On, Reduced-Power, Intermediate, Off
Intermediate = minimum state-retaining power
States track following data
Current state capabilities (booleans)
Power Parent requirements
Power Children requirements
Power state structure version

18. Memory Power Management
When processor is idle
For a short time...
For a long time...

19. HDD Power Management
When is it worth it to power down the HDD?

20. Wifi Receiver Power Management
Computer / router cooperation
Router information buffer

21. Thank You!