What is a System Management Unit?

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  • Written By: Malcolm Tatum
  • Edited By: Bronwyn Harris
  • Last Modified Date: 04 October 2019
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System Management Units, also known as SMUs, are a relatively new form of control subsystem. The units first appeared with Mac systems in the latter part of 2004. Essentially, the System Management Unit is a form of microcontroller that is located on the logic board of the equipment. The SMU works in conjunction with the operating system installed on the device, and helps to adjust the operation of several key operations.

The System Management Unit was designed to replace the older power management unit found in older Mac products. The newer device was designed to encompass all the functions of the older PMU, and also take over a few other essential processes as well. The idea behind combining all these functions into one central unit was to enhance the power functionality of the computer models.

Working as an advanced internal subsystem, the System Management Unit takes orders from the operating system installed on the computer hardware. The operating system monitors the activity level of all the subsystems that make up the computer and communicates the status back to the SMU. In turn, the System Management Unit implements changes to power flow or speed in order to prevent any components from overheating or using excess energy.


There are several key components that are adjusted by the System Management Unit. The hardware will receive commands generated by the SMU to adjust the operation mode of the system from on to off, or from a waking state to an idle state. In addition, the unit will send commands to adjust the speed of the cooling fan, and will control the process of resetting different programs.

Like any computer component, the System Management Unit can sometimes malfunction. When this happens, it is possible to reset the SMU manually and resolve any issues resulting from that malfunction. When performing a manual reset does not eliminate the problems, the manufacturer provides several alternate solutions that may be employed before replacement of the SMU becomes necessary.


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