The Asus 1215n netbook is very picky when it comes to memory upgrades. I purchased two of these CM3X2GSD1066 2GB modules and they work flawlessly. All 4GB is recognized in x64 Windows once you upgrade the BIOS to 0604. Corsair is one of the most respected names in the business, and to top it off they offer a lifetime warranty. I've had to RMA a few different modules over the years and their RMA service is outstanding.