Phenom CPU have two individual memory controllers DCTs, each one of them controls single memory channel 64 bit. These two DCTs can work simultaneously when memory modules are installed on different memory channels. It is called “unganged mode”.
You can switch to “ganged mode, 128bit” when you are using two or four of the same memory modules. Please kindly enter BIOS setup program, to press CTRL+F1 key to enable advanced BIOS setup features then enter "MB Intelligent TweakerM.I.T.\ DRAM Configuration", to set the “DCTs Mode” as “Ganged”.