Double Parity

I recently upgraded my Macbook Pro to 4GBs of RAM. My previous Apple laptop – a Powerbook – was notoriously finicky with non-Apple RAM, so I’m conditioned to thoroughly test my system after a memory upgrade, to make sure the system is fully functional and stable.

On PCs, my preferred test software is an open-source application called Memtest86+. It’s easy to put a copy of the application on a bootable flash drive or CD, restart the system, and let it run. On the Mac, it’s not quite as simple. Memtest86+ has been ported to OS X, but even though Memtest86+ is free, the MemtestOSX developer charges US$1.39 per download.

Now, I know that US$1.39 is pretty meager, but I still found it distasteful. Initially, I thought this was a violation of the GPL, but each download includes the MemtestOSX source code, so I believe the GPL is satisfied. Also, while I realize that bandwidth does cost money, there are plenty of places (Google Code, SourceForge, etc.) where the developer could host his project for free. Needless to say, I could not bring myself to fork over the cash.

Fortunately, there is another alternative. Kelley Computing has an application called Rember – a front-end GUI for the command-line based MemtestOSX. But it also includes MemtestOSX itself! It’s not quite the latest version, but it is fairly up-to-date. You have to dig a little to find it, but it’s there and freely available.

The trick with testing RAM is that you want to test as much of the RAM as possible. If you have OS X running and applications open, you are not going to be able to test a significant portion of your memory. The best option is to restart your computer into single-user mode by holding down command-s during startup. This brings the computer into a minimal console environment. It is so minimal that power management is not even enabled, so it’s likely that your system fans will be spinning pretty loudly. No worries…start MemtestOSX and let it test away.

$ ./Applications/Rember.app/Contents/Resources/memtest all 3

On my 4GB system, it took a little over 3 hours to run a 3-pass test.

Note: When I ran memtest, it grabbed most of, but not all of the available memory. So I just canceled the run, and restarted it in the background.

$ ./Applications/Rember.app/Contents/Resources/memtest all 3 &

Then I launched a second instance of memtest, which grabbed and tested the remaining memory.