There are two Integrated Memory Controller in AMD Phenom II CPU die. Here is Deneb CPU (Phenom II x4) Diagram that shows two discrete bidirectional links.
Ok this is not that hard, I try to make you understand
First I want you to be confirmed that both ganged and unganged modes are DUAL Channel mode of different types
As I've read a post by some user somewhere in this forum that Ganged is for dual channel and Unganged is for Single channel. <- This line is totally wrong.
When you set Ganged mode, A set of two cores of your quad core CPU uses one Memory controller, similarly remaining two cores uses other Memory controller. In this case both memory controller are running concurrently, that is why it is dual channel too. But In this case, data access limit for each core is limited because each two cores are using different memory controllers. Theoretically this mode is suitable for Single thread applications.
Ex: Core 1 and core 2 can use only first memory controller.
and Core 3 and Core 4 can use only second memory controller.
And When you set Unganged mode, this means every core in your CPU has full access to both memory controller. In this case too both memory controller is running concurrently, and hence they are running in Dual Channel mode too. But in unganged mode, each two core are not limited to use one memory controller. To get optimum performance with multithreading application, unganged mode is more suitable.
Ex: Core 1, Core 2, Core 3 and Core 4, all can access data (read/write) from both memory controller anytime.
However its all mathematical and theoretical. To differentiate/measure performance between both modes within real world operations, observer will really need to adapt their mind and eyes as a very high precision clock. Mostly Unganged mode is perfect to obtain optimum overall speed.