Apple Hardware Test
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Apple Hardware Test (AHT) contains a suite of diagnostics that will test the hardware of your computer. It's a great way to rule out a hardware issue when troubleshooting your computer.
To start up your computer in AHT:
• Shut down your computer
• Press and hold the D key
• Press the power button to turn on your computer
Computers that shipped with OS X Mountain Lion (or later versions of OS X/macOS) support the use of AHT over the Internet. These computers will start up to an Internet-based version of AHT if the hard drive does not contain AHT. An Internet-enabled connection via Ethernet or Wi-Fi is required to use this feature. To start up to an Internet-based version of AHT:
• Shut down your computer
• Press and hold Option (Alt) and D
• Press the power button to turn on your computer
If the Apple Hardware Test indicates that the RAM memory is faulty you should be able to find instructions on how to replace it in your computer’s manual without voiding the warranty. However, if the problem is related to any other component the only option is usually to hand over the computer to Apple.