People shouldn't get confused between the number of cores active while running Dolphin and the actual number of major threads Dolphin uses. Like rpglord said, Dolphin will use at most 3 major threads to do the majority of its processing. One thread handles emulation of the GC/Wii CPU, GPU, and DSP. Note, since the New AX HLE merge, the DSP gets a major thread on HLE just like LLE + LLE on threads.
Dolphin has a number of minor threads for things like input and handling the GUI, but in reality they end up doing far less than what the major threads do. With options like OpenMP it is possible to see more than 3 cores active while running Dolphin. But only 3 threads at most are driving most of Dolphin's performance.
Also, be careful with the Windows task manager rpglord, when measuring how many cores are active. Due to how many versions of Windows handle their scheduling, it may look like all cores are in use, but actually something else is happening. Dolphin's threads tend to jump across cores faster than Windows can report, so in between one reporting interval, Dolphin's threads will have done some processing on a number of different cores (not simultaneously however). Lock Threads to Cores will correct this. We get a number of people with i7s wondering why all 8 of their cores are active but at like 20% or something because of this misconception :p
Dolphin has a number of minor threads for things like input and handling the GUI, but in reality they end up doing far less than what the major threads do. With options like OpenMP it is possible to see more than 3 cores active while running Dolphin. But only 3 threads at most are driving most of Dolphin's performance.
Also, be careful with the Windows task manager rpglord, when measuring how many cores are active. Due to how many versions of Windows handle their scheduling, it may look like all cores are in use, but actually something else is happening. Dolphin's threads tend to jump across cores faster than Windows can report, so in between one reporting interval, Dolphin's threads will have done some processing on a number of different cores (not simultaneously however). Lock Threads to Cores will correct this. We get a number of people with i7s wondering why all 8 of their cores are active but at like 20% or something because of this misconception :p