Explainer: System Management Controller (SMC)

From the earliest Mac, Apple’s hardware has relied on a combination of processors and chipsets designed and made by other companies, together with its own custom chips to handle special functions. Among the latter are:

  • the array of sensors in your Mac,
  • control of any cooling fans,
  • the Power button,
  • opening and closing of the lid of a laptop model,
  • sleep, shutdown, and wake,
  • battery charging in laptop models,
  • napping and control of the speed of the processor,
  • some display settings, including Target display mode,
  • recognition of peripherals connected to some ports, including USB-C,
  • any accessory lights.

The custom electronics required to handle those, and more, are located in what’s known as the System Management Controller, or SMC. Prior to the introduction of the T1 and T2 chips, Mac models with Classic 68K, PowerPC and Intel processors relied increasingly on the SMC. A malfunction in any of those systems was a good enough reason to perform a manoeuvre intended to reset the SMC, as detailed here.

This started to change almost five years ago, when the first MacBook Pro featuring one of Apple’s SoCs appeared. Although the T1 doesn’t do as much as the later T2 chip, it supports the Touch Bar, Touch ID, Apple Pay, Secure Enclave, and fingerprint recognition. With the T2 chip, more features of the SMC moved into its more capable circuitry, to the point where T2 Macs need a special reset manoeuvre to accomplish their equivalent of resetting the SMC.

Last year all changed again, as there’s no SMC at all in an M1 Mac. Instead most of its functions are performed within Apple’s new SoC, by a part known as the Always On Processor (AOP). This is a cut-down basic ARM core with its own firmware which remains powered-up and active even when the main cores are sound asleep. It runs the Apple Silicon version of power management software too, according to the settings in your Energy Saver pane, and the pmset command tool.

The theory goes that M1 Macs not only can’t reset their non-existent SMCs, but you wouldn’t want them to if they could. Now if you suspect a problem with features previously associated with the SMC, you should be able to check and correct its settings manually without the need to reset anything. If it still seems wonky, what you should do is shut your Mac down, disconnect all non-essential third-party peripherals and the mains power lead, wait a minute or so, then start your Mac up again. The AOP should be re-initialised soon after startup, load its firmware, and be ready to work normally again.

Gone are the days of resetting the SMC as a universal panacea. We’ll just have to come up with another magic solution as a replacement: pass me the lucky rabbit’s foot and put cucumber slices on my trackpad.