Your machine’s SMC (System Management Controller) stores settings in relation to power management, temperature monitoring, fan control, status lights, keyboard backlights, and a few other miscellaneous components. If your SMC is experiencing problems you might notice things like excessive fan noise, slow performance, slow battery charging, sleep/wake problems, and random shutdowns.
Fortunately, resetting SMC is incredibly simple:
- Disconnect the power cord
- Either from the Mac or from the AC outlet.
- Wait 15 seconds.
- Plug it back in.
- Then wait another 5 seconds.
- Turn your machine back on.
- Portable Macs with non-removable batteries
- Shut down and unplug your Mac.
- On the built-in keyboard, press and hold the SHIFT + OPTION + CONTROL + POWER buttons for 10 seconds.
- Connect the power adapter.
- Turn the Mac on normally.
- Portable Macs with removable batteries
- Shut down your Mac.
- Disconnect the power cord and remove the battery.
- Press and hold the POWER button for 5 seconds.
- Put the battery back in.
- Reconnect the power cord.
- Turn the Mac on normally.
PRAM (Parameter Random Access Memory) refers to a small amount of special, battery-backed memory in every Mac that stored information the computer needed before it loaded the operating system. Modern Macs no longer use PRAM; they instead use something called NVRAM (Non-Volatile Random Access Memory). NVRAM serves approximately the same purpose as PRAM, but now contains only a few functions: your selected startup disk, speaker volume, screen resolution, time zone, and—if your Mac has crashed recently—details of the last kernel panic.
If your Mac seems to take forever to figure out which disk to boot from, if it starts up with a different screen resolution, has weird audio problems (no sound, grayed out volume control menu), or has experienced a kernel panic; resetting the NVRAM is recommended.
- Shut down your Mac.
- Press POWER, then hold COMMAND + OPTION + P + R for 20 seconds.
- Let go and allow your Mac to continue starting normally.
- If you have an older Mac that chimes at boot, hold down the keys until you hear a second startup chime.
- Check the Startup Disk, Display, and Date & Time panes in your System Preferences to make sure they’re set the way you want them.
If you hold down COMMAND + OPTION + P + R and see nothing but a gray screen that doesn’t change for several minutes, don’t panic. Disconnect all USB devices (except your keyboard)*, hold the power button down until the Mac shuts off completely, and then press it again and immediately hold down COMMAND + OPTION + P + R.
*If that doesn’t work and you’re using an external Bluetooth keyboard, try using a USB keyboard instead.