Summary

The System Management Controller (SMC) is a chip on the logic board that controls all power functions for your computer. If your computer is experiencing any power issue, resetting the SMC may resolve it. The SMC controls several functions, including:

* Telling the computer when to turn on, turn off, sleep, wake, idle, and so forth.
* Handling system resets from various commands.
* Controlling the fans.

Products Affected

Mac Pro

Note that resetting the SMC does not reset the PRAM. Resetting the SMC will not resolve issues in which your computer is unresponsive—in these situations, restarting your computer will generally suffice. If your computer isn't responding, perform these steps one at a time, in this order, until the issue has been resolved:

1. Force Quit (Option-Command-Escape).
2. Restart (Control-Command-Power).
3. Force Shut Down (press the power button for 10 seconds).

Resetting the SMC can resolve some computer issues such as not starting up, not displaying video, sleep issues, fan noise issues, and so forth. If your computer still exhibits these types of issues after you've restarted the computer, try resetting the SMC.

To reset the SMC on a Mac Pro:

1. From the Apple menu, choose Shut Down (or if the computer is not responding, hold the power button until it turns off).
2. Unplug all cables from the computer, including the power cord and any display cables.
3. Wait at least fifteen seconds.
4. Plug the power cord back in, making sure the power button is not being pressed at the time. Then reconnect your keyboard and mouse to the computer.
5. Press the power button to start up your computer.

Another way to reset the SMC on a Mac Pro computer is:

1. From the Apple menu, choose Shut Down (or if the computer is not responding, hold the power button until it turns off).
2. Open and remove the metallic outer door.
3. Press the SMC_RST switch that is located slightly below and to the right of the row of diagnostic LEDs. Use a non-metallic, non-conductive object, such as a wooden pencil. Note: Mac Pro (Early 2008) does not have an SMC_RST switch, refer to the reset procedure steps in the previous section.
4. Replace the metallic outer door.
5. Press the power button to start up your computer.

Unlike models of Power Mac G5 or Power Mac G4 computer, the Mac Pro computer does not have a PMU. This functionality has been replaced by the SMC.