We previously noted that one of most common culprits of general system instability, problems installing or re-installing Mac OS X, and various other issues is defective RAM. Some incremental Mac OS X updates in particular have been noted as being "picky" about installed memory.
Just last week Hewlett Packard announced that it had discovered a design flaw in some third-party memory modules used in notebook PCs across the industry. The company already instituted a voluntary replacement program to quickly service customers who may be affected by the issue
With this news circulating, it might be a good time to revisit some aspects of faulty RAM and its effect on various Macintosh models.
You can sometimes determine if you have a "bad" RAM module by using the Apple Hardware Diagnostic CD, included with all currently shipping Macintosh models. To use the Apple Hardware Test CD, restart your computer while holding down the C key until the "Loading..." icon appears.
Note that the Apple Hardware Test can not be used when a mouse is directly connected to the USB port on the display or on the iBook. Apple says "Please connect the mouse to a USB keyboard."
However, sometimes RAM that appears fine to Hardware Test is still defective. This is rare, but it certainly does happen. The most foolproof way to figure out if bad RAM is a cause of problems is of course to remove RAM (replacing it with known good RAM, if necessary) and see if the problem goes away. That being said, the Hardware Test CD is a quick and easy "first step" to take.
Unfortunately, it appears that Apple semi-frequently ships Macs with at least somewhat defective RAM modules. Apple does not disclose its component suppliers.
While browsing through the eJournal of Dan Gillmor, an editor with the San Jose Mercury News, we found this case example of a "bad" RAM headache:
"I have a dual-processor G4, 800 MHz, purchased new. For nearly a year I had intermittent crashes, freezes, memory problems, app shutdowns, you name it. I reinstalled the entire system numerous times. 75% of the time I couldn't even get the OS reinstalled, I'd have to try 3-4 times to reinstall it. I could never get a good incremental upgrade past 10.2.3. It was very frustrating.
"One day about a month ago, I was pawing through the stack of disks that Apple provided with the computer, which I had never opened. It was the HW diagnostic disk. I decided 'What the hey' and ran it. Immediately it identified that I had a bad RAM DIMM. I remembered that I had mail-ordered a new DIMM about the time that the crashes started.
"I removed the DIMM, going back down to 512MB, and all was immediately well. I then went out and purchased another new 512MB DIMM locally at a store (in case it was bad and I needed to return it). Installed it and all has been well since. I have not had a single crash, kernel panic, or any other (strange) behavior since [...]"