The System Management Controller (SMC) is a subsystem of Intel processor-based Macintosh computers. It is similar in function to the older SMU or PMU of non-Intel Macintosh computers.
Overview
The SMC has roles in controlling thermal and power management, 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.
References
System Management Controller Wikipedia(Text) CC BY-SA