System Management Controller
The SMC has roles in controlling thermal and power consumption, battery charging, video mode switching, sleep and wake, hibernation, and LED indicators. It also enables enforcement of the Mac OS X End User License, allowing it to identify when it is running on non-Apple hardware.
Apple releases occasional model-specific updates to SMC firmware which correct bugs and defects in the system.
Corrupted SMC firmware, whatever the cause, is not entirely uncommon and may lead to operational problems. Resetting the SMC may resolve certain issues, such as:
- Cooling fans running at constant high speed
- Computer running slowly despite low CPU load
- Failure to recognize keyboard or trackpad
- Failure to recognize add-on hardware or peripherals
- Failure to recognize battery
- Failure to wake from sleep, or unexpected sleep
- Sudden unexpected power loss
- Non-responsive power button
- Poor battery performance
- Non-operational LED indicators
Resetting the SMC is usually accomplished by removing all power from the system for a period of time (by unplugging the mains connector or removing the battery) or by operating the power button in a special way. Apple provides model-specific instructions for SMC reset.