The System Management Controller (SMC) is responsible for many low-level functions on Intel-based Macs. These functions include:
Responding to presses of the power button
Responding to the display lid opening and closing on portable Macs
Battery management
Thermal management
The SMS (Sudden Motion Sensor)
Ambient light sensing
Keyboard backlighting
Status Indicator Light (SIL) management
Battery status indicator lights
Selecting an external (instead of internal) video source for some iMac displays
Note: Resetting the SMC does not reset, or otherwise change, the contents of PRAM, which is also known as NVRAM on Intel-based Macs.