Well, like the title says. I have an Alienware M18xr2 with 4 8gb crucial ram 1 cards reads 1333mhz, and the other 3 read at 1600mhz in Intel extreme tuning utility. The were purchased in pairs, and should be perfectly compatible with each other. I have a 330 power supply, 3940xm, 780m, and windows 7 ultimate. Is there anyone out there who has seen this before or that knows what causes this. I've tried moving the cards around and even only using 2 cards, but it will aways have 1 card that reads at 1333. I've been in the bios, and everything.