Memtest and Memtest86
Memtest and Memtest86 are software utilities that scan and test computer memory chips (RAM) for any defects or errors. Many computer professionals and repair technicians use Memtest86 to test RAM due to its reliable and accurate scan results. They are both open source programs, meaning they are free to use. Memtest86 is a DOS-based program and includes a variation called Memtest86+. Both are actively updated to work with older 386 and 486 computers on up to the current dual and quad-core computers. Memtest86 was originally developed by Chris Brady and Memtest86+ was developed by Samuel Demeulemeester.
Memtest is a variation of Memtest86, with the main difference being that it runs in the Windows environment. It's compatible with Windows 95 through Windows 7 and allows you to define the amount of memory to be tested.
Also see: Memory definitions