Is Your Memory Failing?
As most of you know last August or September I purchased a new G5 to replace the Blue-and-White G3 that had come to be known as FrankenMac. For the first time in my Mac computing life I would own a Mac while it was still one of the current machines. This was going to be sweet.
For the first few weeks everything was fine. The machine was everything I had hoped it would be. The only danger was that while sitting slack-jawed in front of this new speed demon I might drool on the keyboard and short something out. Then the trouble started.
Trouble in Paradise
The first sign of trouble came while trying to create a DVD using iDVD 4. I could create very short DVDs, but longer ones would cause iDVD to crash during the encoding process. Sometimes the crash would occur immediately after starting to create the menus. Usually iDVD was the only application affected, but sometimes I would see the dreaded kernel panic screen. You know, the black-and-white text screen that tells you, in several different languages, to restart the computer. Other applications that I use every day, such as Safari and Microsoft Word, were performing quite well. Photoshop was also working well, although I hadn’t tried anything that would really push it.
At this point I was starting to doubt my Mac knowledge. Maybe a dual 2 GHz Mac with 1.5 GB of memory just wasn’t enough machine to work well with about 70 minutes of video? That’s when the second symptom started to occur. Booting the system from scratch took four or five attempts, with each of the failures greeted by a kernel panic. Once the system finally started, everything went wonderfully as long as I didn’t try to run iDVD or Final Cut Express. Something was wrong and the boot-up problems were starting to convince me it might be hardware-related, since the kernel panics were occurring before any software had time to load.
Identifying the Culprit
I knew from reading posts in numerous forums that kernel panics are often the result of some hardware problem. Time to do a little troubleshooting. Without going into a lot of detail here, since that’s not the point of this article, the boot problems were apparently due to a loose card inside the computer. Once that was resolved I could get back to editing video right? Wrong. Problems with iDVD and Final Cut Express persisted.
After putting my project aside for a while, I stumbled on a potential answer one day. In one of the Mac forums I ran into someone who was doing a similar project on a Mac with less memory. Several messages later, he and I concluded that perhaps I had some bad memory chips. Time for more testing.
Trial and Error
If you suspect that your problems are due to bad memory, there are several methods available for testing. One common method is to remove a chip or two, boot the system, and attempt to duplicate the problem. Presumably if the problem persists then the bad RAM is still in the system. If the problem is gone, then the bad RAM is among the chips that have been removed. You are essentially using repeated trials and the process of elimination to help solve the mystery.
You would think that this method would appeal to someone like me. Not so. I have a few problems with this method. First, it is very time consuming and requires a great deal of your attention since it may be necessary to take the system apart several times. Second, you must know how to safely remove components from your Mac. Finally, it requires more knowledge about your Mac than some users want to know. Some Macs have RAM slots that are difficult for users to access while others, like my G5, require that RAM be installed in pairs. Finally, you might actually damage a good chip if it is not carefully removed and replaced.
Users who have only a little more than the minimum amount of RAM required for OS X may face an additional problem using this method. Removing RAM, even if your Mac permits removing one chip at a time, may leave you without enough memory to boot the machine.
If you are uncomfortable taking your machine apart several times, there is another option: software-based memory tests. Testing memory using software is not infallible; it’s almost impossible to test every state of memory. Although it’s not perfect, software-based memory testing is a useful tool.
If your computer shipped with an Apple Hardware Test CD, that’s a good place to start. If a bad chip is identified, it can also pinpoint the slot that chip currently occupies. I didn’t have access to that disc during testing, but it can be a useful tool.
One of the first software tests that I tried was Tech Tool Pro 4. I decided to let it run all of the tests simply to check the overall health of my system. I expected it to find memory errors, but none were found. Normally that would be great news but the application crashes and occasional kernel panics were still occurring while working with large files.
Rember to the Rescue
Searching the Net I came across a tool called Rember. The program essentially provides a graphic user interface to a command-line memory testing tool called memtest. Upon launching Rember, the user is faced with the main Rember tab. From here you can control whether Rember tests all or part of the memory you have installed. You can also control the number of times the test is repeated. Although it is a good idea to run these tests several times, keep in mind that this can be a time-consuming process.
The right side of the main tab also presents you with an option to “Quit all applications.” Checking that option also lets you choose an option to quit the Finder. During testing I usually choose both of these options. Doing so frees up more memory for testing. The second tab, called Logs lets you see the results of testing. In my case, Rember began identifying errors almost as soon as the test started.
I also used memtest directly. memtest is the same core code that Rember uses. The principal difference is that memtest is a command-line utility that can be run in single-user mode. This allows it to test areas of memory that would normally be occupied by OS X. Even if you are unfamiliar with the command line, this might be a good choice. The directions included with this program are fairly easy to follow.
Installation is of memtest is easy, since it is installed using a standard OS X installer package. Once the program is installed, it can be run by completing the following steps:
Boot the system in single-user mode by holding down Command-S as the system boots. Once you see text scrolling by, it’s safe to let go.
Now you can run memtest by typing:
/Applications/memtest/memtest all 3 -l
In this command, the text before the word all is the path to memtest. If you have not installed it in the default location, you will need to enter a different path. The word all tells the program to test all available memory. The number indicates how many times the test is to be run, and the -l tells memtest to place the results of testing in a log file. That file will be located in the same folder as memtest.
If you try to test all available memory and test results do not start appearing on the screen almost immediately, there may be a problem. Under some circumstances, Darwin does not appear to like the all part of the command. In that case, repeat the startup procedure replacing all with a specific amount of memory to test. In essence you are replacing all the the number of megabytes of memory to test. Although I can’t give you a definitive number for the upper limit the documentation suggests entering a value that is two or three percent less than your total memory.
The output from Rember and memtest will report the results of testing, as well as the memory address of any errors. The addresses are reported in hexadecimal notation. I’m not very good at converting these number to specific chips, but at least I know there is likely to be a problem. I’m going to start by pulling the pair of chips that were installed as an upgrade.
I expected Rember and memtest to yield the same results and have the same problems testing all memory because they are essentially the same test engine. Having said that, I am left with a puzzle. These two programs are reporting memory errors and Tech Tool 4 is not reporting errors. Which one is right?
I like Tech Tool Pro 4, but in this case I think there may be some memory errors creeping into my system. If my system were performing memory-intensive tasks better, I would think maybe Tech Tool was right. I guess it’s time to start shopping for memory.
Also in This Series
- Give Alert Sounds a Little Personality · March 2012
- Create Your Own iPhone Ringtones · February 2012
- Create Your Own Homemade Audio Book · December 2011
- Upgrade to Lion Painlessly · August 2011
- Make the Most of TextEdit · July 2011
- Using the Free Disk Utility on Your Mac · May 2011
- Making Use of QuickTime X · March 2011
- Making the Most of What’s Already on Your Mac · February 2011
- Making the Most of What’s Already on Your Mac · January 2011
- Complete Archive