MemTest86+

Memtest86+ is a stand-alone memory tester for x86 and x86-64 architecture computers. It provides a more thorough memory check than that provided by BIOS memory tests. Memtest86+ can be loaded and run either directly by a PC BIOS (legacy or UEFI) or via an intermediate bootloader that supports the Linux 16-bit, 32-bit, 64-bit, or EFI handover boot protocol. It should work on any Pentium class or later 32-bit or 64-bit x86 CPU.

the above is the description from the memtest website. this tool is invaluable for testing RAM when your uncertain of its current quality. windows has a built in one but its not as good as booting from this and running it separately.