Phillip Corcoran said:
You'd best stick with 1333 MHz as shown on Acer's spec sheet: http://www.asus.com/Notebooks_Ultrabooks/X44H/#specifications
So I bought the 1333Mhz G-Skill mentioned above. Still my laptop shows 2Gb Ram instead of 4Gb.
CPU-Z shows 2Gb as well. My OS is Win 8 64bit. Didnt had any setting in BIOS. Applied 4096 Max Memory in Advanced Boot option, still no result.