The Apple Hardware Test

The Apple® Hardware Test is an important troubleshooting utility which has been shipping with new Macintosh® computers since 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 an extract from the "Hardware Testing" chapter of our book, Troubleshooting Mac® OS X.

Running the Apple Hardware Test

The Apple Hardware Test was originally distributed on a separate Apple Hardware Test CD. The latest Macs distribute the Apple Hardware Test on a special volume on the Software Restore and Install DVD. This DVD, part of the discs that shipped with your Mac, is often labeled Mac OS X Install Disc 1. 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 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 using either of the following methods:
     • Select Restart in the Apple menu.
     • Press the Command-Control-Eject keyboard combination.
  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.
• If your PowerPC™-based Mac has an Apple Hardware Test volume on the Software Install and Restore DVD, aka Mac OS X Install Disc 1:

1. Insert the Software Install and Restore DVD that came with your Mac into your Mac's optical drive.
2. Restart your Mac using either of the following methods:
   • Select Restart in the Apple menu.
   • Press the Command-Control-Eject keyboard combination.
3. Immediately press and hold the Option key on your 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 continue to start up from the Apple Hardware Test volume.

• If you have an Intel®-based Mac, see the AppleCare Knowledge Base document "Intel-based Macs: Starting up into Apple Hardware Test."
• Otherwise, consult the printed manual that accompanied your Mac for instructions on how to use the Apple Hardware Test that shipped with your computer.

After you startup from the Apple Hardware Test, run the Extended Test.

You may want to run the Extended Test several times in a row as sometimes intermittent problems don't show up on every 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.

We have read of cases where RAM problems did not show up until nearly 40 loops, so give it a good run.

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 4 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 which 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: If you are using Mac OS X 10.4 Tiger™, use only the hardware tests of third-party utilities that combine hardware testing and disk utilities, such as TechTool Pro 4 and TechTool Deluxe, unless the version of your third-party utility includes Tiger-compatible disk utilities. For example:

• The disk utilities in TechTool Pro version 4.0.4 and later are compatible with Tiger on PowerPC-based Macs, while those in TechTool Pro 4.5.x or later can be used with either PowerPC- or Intel-based Macs.
• Use only TechTool Deluxe version 3.0.4 or later with Tiger on PowerPC-based Macs.

See the AppleCare Knowledge Base document "Only use Mac OS X 10.4-compatible disk utilities with Mac OS X 10.4 volumes."

Related links

• All AppleCare Knowledge Base documents related to the Apple Hardware Test.