the API is still called win32, even when running in 64bit mode... but that is
being nitpicky kartal:
there isn't really any way around booting your system with a dedicated memory tester, if you want anything remotely accurate and thorough. Memtest86 is the tool of choice. Microsoft also has a windows-based tester, but iirc that also has to be booted into, and you might as well use the tried-and-true memtest86 then.