You decided to upgrade your machine with more memory. Unfortunately, those brand new memory modules might have a manufacturing defect or they might have received harsh treatment during shipping or handling. It’s a good idea to test out that new memory as soon as you’ve installed it so that you can take advantage of the manufacturer’s warranty sooner rather than later.
Testing memory is not as simple as plugging it in and seeing if your machine boots up properly and correctly reports the new memory size. The nastier bugs with bad memory are buried deeper inside the memory modules and don’t become apparent until they are stressed under heavier workloads.
Fortunately, bootable software diagnostic tools for Mac/PC/Linux systems such as Memtest86 are available that put your new memory through the paces with an onslaught of tests designed to expose bad memory. The various algorithmic tests invoked by these tools — all with cool-sounding names like Moving Inversions, Modulo 20, Bit Fade, and Hammer — are usually run with multiple passes for additional test coverage.
The only drawback is that these tests can take a very long time to run. The total runtime depends on your CPU speed, your memory speed, your motherboard chipsets and the amount of memory installed. It’s not uncommon for a full run of Memtest86 with all the default settings to take 20 hours or more. Even though it may require leaving your machine running overnight, a full memory test provides the peace of mind that your brand new memory is indeed working as advertised and not causing any difficult-to-debug issues, crashes or data corruption.