How Many USB Controllers Are in the Late 2014 Mac Mini?

I am transferring a lot of data to a large number of iPads from a Mac Mini, over USB. I am finding that the late 2014 Mac Mini is significantly faster at completing the transfer than the Mid 2011 model.

If it's relevant - I'm connecting to iPad 2s.

I think I can rule out any CPU / Ram differences.

Have Apple added more USB controllers to the new Mac minis? My understanding is that the old models had 2 controllers, is it possible that the 2014 model has 4?