Testing RAM
From Mac Guides
Not all RAM is created equal. Some brands and types will work flawlessly, while others will not. Some memory is so bad that it's obvious: the machine won't boot, or crashes almost immediately. Others can be more subtle, silently corrupting your data in ways that you may not notice until it's too late. It is recommended that you test any new memory (or the existing memory in a new computer) as soon as it's installed.
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Apple Hardware Test
While the Apple Hardware Test CD or DVD that comes with every new Mac includes a memory tester, it is widely regarded as inadequate. Many machines with real memory problems will erroneously pass the tests done by the Apple Hardware Test.
Memtest
Memtest performs a very thorough set of tests designed to uncover even the most subtle memory flaws. It has a US $1.39 download fee as of November 2006.
- Memtest is a Command Line application, but the supplied documentation will walk you through the process even if you're unfamiliar with the Mac OS X command line.
- It is best used in Mac OS X's single-user mode, so follow the instructions provided with Memtest to restart your Mac in single-user mode.
- Run the program for several iterations, as suggested in the Memtest documentation.
- Depending on the speed of your Mac, the amount of memory installed, and the number of test iterations, Memtest may take several minutes to several hours.
- Once you're finished, you can restart to a normal bootup by typing reboot at the command prompt.
Memtest Alternatives
There are some free alternatives to Memtest:
- Rember is a graphical user interface wrapped around an older version of Memtest. It may be easier for inexperienced users, but comes with a couple of drawbacks:
- It uses an older version of Memtest which may not contain the very latest memory checking algorithms.
- It must run while Mac OS X is fully loaded and using more memory, which means that it cannot test as much of your memory as Memtest can in single-user mode.
- Memtest is released under the free GNU General Public License, so you might be able to find an older version that is free to download somewhere else.
- You can build memtester from source by going through a simple "make" step, as described on the website and in its README file. Once built, you still need to boot into single-user mode by holding down Command ("Apple") and "S" buttons during startup, "cd" into where you placed memtester, type "top" to find out the amount of available memory, run memtester and reboot afterwards by typing "shutdown -r now"
Test Results
If you completed all testing with no errors, congratulations! Sit back and enjoy your new memory. If there were errors, check your warranty status and/or seller's return policy. The memory chips should be exchanged for ones that work.
