Most of your Mac is operated by software which is loaded from your startup volume. 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. These include the EFI firmware, the SMC, NVRAM and (in certain models) the T2 chip.
In Macs without a T2 chip, the SMC is a custom chipset with its own firmware which may sometimes be updated separately from the EFI. This controls many of the extended hardware features like cooling fans. 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. Mac models which include a T2 chip – all current models apart from the iMac – incorporate SMC functions within that chip… How you reset the SMC depends on the Mac, with different routines for laptops with and without a removable battery, and for desktops.
Resetting the SMC and NVRAM are not panaceas for every problem. They will not fix disk problems, nor failing graphics cards. Used appropriately, they can transform a Mac which seems to be dying into one that is in fine fettle.
MacDailyNews Take: If you’ve got seemingly goofy things happening with your Mac’s cooling fans, USB-C peripherals, Sleep issues, poor performance, etc., Howard’s article is your first stop.
[Thanks to MacDailyNews Reader “Fred Mertz” for the heads up.]