Determining Whether the Power Manager Is Present
You can use the Gestalt function with the gestaltPowerMgrAttr selector to determine whether the Power Manager is available and whether certain other devices in the computer can be put into the sleep state. The Gestalt function returns a 32-bit field that may have some or all of the following bits
set:
gestaltPMgrCPUIdle //CPU can idle
gestaltPMgrSCC //can stop SCC clock
gestaltPMgrSound //can shut off sound circuits}
If the gestaltPMgrExists bit is set, the Power Manager is present. If the gestaltPMgrCPUIdle bit is set, the CPU is capable of going into a
low-power-consumption state. If the gestaltPMgrSCC bit is set, it is possible
to stop the SCC clock, thus effectively turning off the serial ports. If the
gestaltPMgrSound bit is set, it is possible to turn off power to the sound
circuits.