How you reset the SMC depends on the Mac, with different routines for laptops with and without a removable battery, and for desktops. the Sudden Motion Sensor (SMS), ambient light sensing, and selection of an external video source for some iMacs.target display mode if this does not work properly, or it switches unexpectedly, suspect the SMC.napping and processor slowing if your Mac performs very poorly but the CPU is not showing high load, suspect the SMC.battery charging (laptops), and the MagSafe power adaptor light.sleeping and shutdown if your Mac sleeps or shuts down when you don’t think it should, suspect the SMC.opening and closing the lid of a notebook.power button if this is not a mechanical problem (older models), suspect the SMC.accessory lights, such as keyboard backlighting, status indicator light, battery indicator lights on non-removable batteries, those around the I/O ports on recent Mac Pros.the cooling fans if these seem stuck full on even when your Mac is just idling, then that is suggestive of an SMC problem.The features which are controlled by the SMC are: Apple explains these in its article on the SMC. Aside from ensuring that its firmware is kept up to date (as for EFI firmware), the SMC may on occasion need to be reset when one or more of its functions has gone awry, such as the fans are stuck on full blast all the time. This chip(set) controls some of the extended hardware features like the cooling fans.
The System Management Controller (SMC) is a custom chip(set) with its own firmware which may sometimes be updated separately from the EFI.
These days any updates should be delivered via the App Store, and Apple explains how to check that yours is up to date in this article, which contains links to updaters if you need them.
Some models have updates which patch bugs and other issues in their EFI firmware. These include the EFI firmware, the SMC, and NVRAM.Įxtensible Firmware Interface (EFI) firmware is the runtime environment that gets your Mac going. But in order to boot it up sufficiently to be able to load that up, and to enable certain hardware features controlling the cooling fans, battery charging, etc., every Mac has firmware and persistent storage for some key settings. Most of your Mac is operated by software which is loaded from your startup disk.