The Apple Hardware Test

The Apple® Hardware Test is an important troubleshooting utility that began shipping with new Macintosh® computers sometime in the year 2000. If your Mac predates the inclusion of the Apple Hardware Test, see the section "My Mac predates the Apple Hardware Test" below.

This FAQ is based on the "Hardware Testing" chapter of our book, Troubleshooting Mac® OS X.

Running the Apple Hardware Test

The Apple Hardware Test was originally distributed on an Apple Hardware Test CD. It is now distributed on a special volume on the Mac OS X Install Disc 1 DVD included with the computer. Each Apple Hardware Test is specific to the type and model of Mac with which it was distributed.

To run the Apple Hardware Test, you must start up from the disc or volume containing the test:

If you have: Then:
An Apple Hardware Test CD:

Start up from it as you would any other bootable disc:

1. Insert the Apple Hardware Test disc that came with your Mac into your Mac's optical drive.
2.

Restart your Mac by either:

  • Selecting Restart in the Apple menu.
  • Pressing the Command-Control-Eject keyboard shortcut.
3. Immediately press and hold the C key on your keyboard.
4. Release the C key after the Apple Hardware Test appears on your display and indicates that it is loading.
An Intel®-based Mac:

See the AppleCare® Knowledge Base document "Intel-based Macs: Using Apple Hardware Test."

Note: If you have a MacBook Air®, see the AppleCare Knowledge Base document "MacBook Air: Using Apple Hardware Test."

A PowerPC™-based Mac with an Apple Hardware Test volume on Install Disc 1:
1. Insert the Install Disc 1 DVD that came with your computer into its optical drive.
2.

Restart your Mac by either:

  • Selecting Restart in the Apple menu.
  • Pressing the Command-Control-Eject keyboard shortcut.
3. Immediately press and hold the Option key on the keyboard. This invokes the Startup Manager.
4. Release the Option key after the Startup Manager appears on your display.
5.

When the wristwatch progress indicator disappears — indicating that the Startup Manager's scan for bootable volumes has completed — select the Apple Hardware Test volume.

For an illustrated example, see the AppleCare Knowledge Base document "PowerBook G4 (17-inch): How to Run Apple Hardware Test."
6. Click the right-pointing arrow. Your Mac will start up from the Apple Hardware Test volume.
None of the above: Consult the printed manual that accompanied your Mac for instructions on how to use the Apple Hardware Test that shipped with your computer.

After starting up from the Apple Hardware Test, run the Extended Test.

You may want to run the Extended Test several times in a row as intermittent problems may not show up in every execution of the test.

If the test fails, be sure to write down the exact message associated with the failure.

Running the Apple Hardware Test in Loop Mode

Running the Apple Hardware Test in Loop Mode overnight is an excellent troubleshooting step for finding intermittent hardware problems. It is especially useful when troubleshooting intermittent kernel panics.

If Loop Mode is supported by the version of the Apple Hardware Test you are using, you run the Extended Test in Loop Mode by pressing Control-L before starting the test. Looping On should appear in the right window. Then click the Extended Test button.

The test will run continuously until a problem is found. If a problem is found, the test will cease to loop, indicating the problem it found. If the test fails, be sure to write down the exact message associated with the failure.

Intermittent RAM problems may take many loops to appear: let the test run overnight.

If no problems are found after running the Extended Test in Loop Mode overnight, you can stop the Extended Test and exit Loop Mode by either:

  • Pressing the Command-period keyboard shortcut, i.e. Command-.
  • Clicking the Cancel or Stop Test buttons. This can be difficult to do in Loop Mode.
  • Manually restarting your Mac. Restarting manually, i.e. via either the power button or — if your Mac is so equipped — the Reset button, when you have started up from the Apple Hardware Test should not cause problems.

My Mac predates the Apple Hardware Test

If your Mac predates the inclusion of the Apple Hardware Test with new computers, you can use the following third-party utilities to test your hardware:

  • Micromat® TechTool® Pro includes a comprehensive suite of hardware tests applicable to all Macs. TechTool Pro 4.5.x or later is available as a Universal Binary for both PowerPC- and Intel-based Macs.
  • If you purchased an AppleCare Protection Plan, your may have received a Micromat TechTool Deluxe CD that includes some hardware tests. An inexpensive upgrade from TechTool Deluxe to TechTool Pro is available from Micromat.
  • The freeware command-line utility Memtest has been used by many to successfully test RAM. The freeware utility Rember provides a graphical user interface (GUI) to Memtest.

Note: Use only the hardware tests of third-party utilities that combine hardware testing and disk utilities, such as TechTool Pro and TechTool Deluxe, unless the version of your third-party utility also includes disk utilities that are compatible with your version of Mac OS X. In other words, only use disk utilities that are compatible with the version of Mac OS X you are using.

Related links

Did you find this FAQ helpful? You will find a wealth of additional advice for preventing or resolving Mac OS X problems in Dr. Smoke's book, Troubleshooting Mac® OS X.
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