Updated July 2014
Memory test software, often called RAM test software, are programs that perform detailed tests of your computer's memory system.
The memory installed in your computer is very sensitive. It's always a good idea to perform a memory test on newly purchased RAM to test for errors. Of course a memory test is always in order if you suspect that you may have a problem with your existing RAM.
Note: All of the memory testing programs listed function from outside of Windows so each will work no matter if you have Windows (8, 7, Vista, XP, etc.), Linux, or any PC operating system.
Memtest86 is a completely free, stand-alone, and extremely easy to use memory test software program. If you only have time to try one memory test tool on this page, try Memtest86.
While this RAM test is free, PassMark also sells a Pro version but unless you're a hardware developer or other expert, the free download and free basic support available on the site should be enough.
I highly recommend Memtest86!
Windows Memory Diagnostic is a free memory test program provided by Microsoft. Very similar to other RAM test programs, Windows Memory Diagnostic performs a series of extensive tests to determine what, if anything, is wrong with your computer memory.
Important: You do not need to have Windows (or any operating system) installed to use Windows Memory Diagnostic.
Simply download the installer program and then follow the instructions to create a bootable floppy disk or ISO image for burning to a disc like a CD, DVD, etc.
After booting to the disc or floppy disk, Windows Memory Diagnostic will automatically begin testing the memory and will repeat the tests until you stop them. If the first set of tests finds no errors, chances are your RAM is good.
Memtest86+ is a modified and presumably more up-to-date version of the original Memtest86 memory test program, profiled in the #1 position above. Memtest86+ is also completely free.
I would recommend performing a memory test with Memtest86+ if you have any problems running the Memtest86 RAM test or if Memtest86 reports errors with your memory and you'd like a really good second opinion.
It might seem a bit strange that I rank Memtest86+ as the #3 pick, but since it's so incredibly similar to Memtest86, your best bet is to try Memtest86 followed by WMD, which operates differently, providing you with a more well-rounded set of memory tests.
DocMemory Memory Diagnostic is yet another computer memory test program and works very similarly to the other programs I have listed above.
One major disadvantage of using DocMemory is that it requires that you create a bootable floppy disk. Most computers today don't even have floppy drives. The better memory test programs (above) use bootable discs like CDs and DVDs instead.
I would recommend using DocMemory Memory Diagnostic only if the memory testers I have listed above do not work for you or if you'd like yet one more confirmation that your memory has failed.
On the other hand, if your computer isn't able to boot a disc, which is what most of the above programs require, DocMemory Memory Diagnostic may be exactly what you've been looking for.
Note: You must create a free account with SimmTester to have access to the download.