It's advertising . Typically, DDR3-1600 will d fault to 1333 at 1.5 volts. You can manually set it to 1600 but this typically involves using the XMP setting, which oft boosts voltage to 1.65 volts. See manufacturer's instructions on setting manually which *may* require using the 1.65 voltage setting.
An yeah, I know what everybody quotes from Intel saying that anything over 1.5 volts is a bad thing.....however rest assured that using 1.65 volts will not cause your beer to go bad in your refrigerator, your ar to blow its tranny, computer to go up in smoke or a need for you to get a doctor's prescription for ED.
If you comply with MoBo manufacturers stipulations, you have no issues to worry about. And all the MoBo manufacturers will tell you 1.65 volts on SB is just fine and presents no warranty issues.
Sandy Bridge does not demand only 1.5v modules, it will be perfectly happy with 1.65v modules too. If someone tries to tell you that you must have 1.5v modules, then they are either trying to sell them to you, or they have been reading misinformation, or both! Another point to consider here, is that in your BIOS, if you head to the memory voltage setting, and enter 1.5v, the text will remain white/grey, if you enter 1.65v, it will turn yellow, and it isn't until 1.73v that it turns red, so at the moment, I'd rest assured that 1.65v modules are OK to use, and I have had this confirmed by Asus, Gigabyte and Corsair so far, as soon as I hear from anyone else, I will update this again.
Well. Friends thank you all....in the DVD of the main-board , there is a useful utility . i installed it and run it and there was a button for setting a optimum performances.. all of a sudden the PC restart several times and it seems to me that this utility is checking the best performance according to the thermal condition of the system ....after 3 restarts , that utility informed me that you PC can be 30% overclocked...!! after that i saw that my Ram is working on 1666 and my CPU is allowed to work on 4.2 GHZ..!!!
I LOVE ASUS...now it is working really nice....!!!thanks INTEL and ASUS and of course you friends.....