The SMC (System Management Controller) is a hardware component of your computer which is responsible for several low level functions. Sometimes it gets "confused" and needs reset, and how this is done depends on the Mac model you have.
Unfortunately, there are many different ways to do the reset, which are listed in individual entries in this tips database. This entry just explains the SMC in general. Go back to the list, search for SMC, and choose the entry which matches your model if you need instructions on how to do a reset.
These are the main SMC functions, listed by Apple... Battery isn't charging. Mac isn't turning on. Fans are running fast. Mac laptop computer gets too warm. Built-in camera isn't working.
Other sites list these functions... Responds to the press of the power button. Responds to opening or closing the lid of a laptop. Manages laptop battery, including charging, calibration, and displaying power level. Manages the fans to keep the machine cool. Checks the sudden motion sensor to limit damage from drops. Sets lighting of screen, etc based on ambient light. Controls the keyboard backlighting. Controls the status indicator lights. Controls trackpad functions. Controls hard drive power saving, shut down, etc. Selects a video source on iMacs with video input. Controls sleep functions.
Signs the SMC might need reset (some from non-Apple sites) include... Fans are running unexpectedly. Mac is not sleeping or not waking from sleep. Laptops don't sleep when lid closed, or wake when opened. Mac won't startup when the power button is pushed. Power indicator (where available) doesn't display or displays incorrectly. Slow performance even when no obvious process is using the CPU. Battery charging fails or takes longer than expected. USB ports don't work, are slow, don't provide power, etc. Backlighting doesn't adapt to ambient light. Target mode doesn't work. Wifi doesn't work or is reported as not installed. Bluetooth not working correctly.
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