PRAM and SMC Resets: What are they? Both are sets of chips that live on a Mac’s main logic board. They hold information that can become corrupted under certain circumstances which can then cause performance issues. Before resetting the PRAM or SMC for troubleshooting, you should be sure to disconnect any peripherals to ensure that nothing interferes.
But, before explaining how to reset them, I’ll discuss what each does.
PRAM stands for parameter random-access memory. Today, the actual chips used in Intel-based Macs are really NVRAM (non-volatile RAM), a newer technology (think flash drive) that doesn’t require power to maintain information. The old name ‘PRAM’ carried over in general use from the PowerPC days.
PRAM chips hold information between boots on previous computer settings such as speaker volume, screen resolution, some RAM configuration information and current startup disk selection, among a few other odd settings. If your computer won’t boot while connected to a known-good MagSafe adapter and the power light is on on the charger where it connects to the machine, or if you’re experiencing problems that may be related to any of the settings that PRAM controls, then a reset may be needed.
To reset PRAM:
- Shut down your Mac.
- Locate the following keys on the keyboard: Command (⌘), Option, P, and R.
You will need to hold these keys down simultaneously in step 4. - Turn on the computer.
- Press and hold the Command-Option-P-R keys before the gray screen appears.
- Hold the keys down until the computer restarts and you hear the startup sound for the second time.
- Release the keys.
More information on PRAM and resets can be found on Apple’s support page.
SMC stands for system management controller and like PRAM is comprised of chips on the Main Logic Board that control several critical systems on a Mac. These include power (including aspects of sleep), fan speed, and communication with peripherals and internal devices such as the AirPort/Bluetooth and I/O cards, the battery and on laptops the topcase (the keyboard, trackpad and power button), among other functions.
If you are having problems with any of these areas of your computer, an SMC reset may be recommended. However, Apple recommends that the SMC be reset only after all other troubleshooting steps. If those steps fail to correct the problem you’re having, or if your computer simply isn’t powering on while connected to a known-good charger (plugged into a known-good outlet) — even after a PRAM reset — then an SMC reset would be next.
On portables there are two possible ways to reset the SMC. If the battery is removable as on some MacBooks and some older MacBook Pros, just disconnect the power supply, remove the battery, turn the machine over, hold down the power button for ten seconds, replace the battery, plug it back in, and try to turn it on. For machines with non-removable batteries try a keyboard reset by powering the machine off (if it’s functioning), leave the MagSafe adapter plugged in, press at the same time the shift-option-control keys on the left side of the keyboard, and the power button, after a second or so let go. Then try to power it back up if it didn’t do so on it’s own.
On iMacs, Mac minis and Mac Pros, reset the SMC as follows:
- Shut down the computer.
- Unplug the computer’s power cord.
- Wait fifteen seconds.
- Attach the computer’s power cord.
- Wait five seconds, then press the power button to turn on the computer.
More information on SMC resets can be found at the link above, including a list of troubleshooting steps to take beforehand, as long as your machine is functional.