Memtest86+ should be one of those utilities that comes handy when troubleshooting a problem with your PC or server when you suspect experiencing a hardware issue. Also, can help stress testing a new system especially a Server to test if the memory on the system is good and error free.
Memtest86+ and enhanced development of the original Memtest86 is a operating system independent utility based on Linux kernel to test the memory on a server or a PC. Memtest86+ is a bootable image that can be burnt of a CD using the ISO image or from removable media like Floppy disk or a USB flash disk (where supported by the BIOS) and run a complete test on the system memory. This as I said earlier, makes it a Operating System independent utility (not so surprisingly )
When you start the system with a Memtest86+ bootable CD, Floppy or a USB flash disk starts and tests the system memory by writing various test patterns to every single memory address and then read them back and compare for any variations or errors. A variation indicates a problem with the memory address. It can even change memory timings on the fly where supported to test the memory. The newer version can support Core2 Duo & Quad processor based systems.
Memtest86+ is an open source software released under GPL2 license. Memtest86+ can be downloaded from here.