Choose your model
From the Apple () menu, choose About This Mac.
Click More Info.
Select Hardware from the Contents list.
Find "Number of Processors" under Hardware Overview. The quad-core and 6-core Mac Pro have one CPU and the 8-core and 12-core Mac Pro have two CPUs.
2012
Mac Pro (Mid 2012), Quad-core
Mac Pro (Mid 2012), 6-core
Mac Pro (Mid 2012), 12-core
2010
Mac Pro (Mid 2010), Quad-core
Mac Pro (Mid 2010), 6-core
Mac Pro (Mid 2010), 8-core
Mac Pro (Mid 2010), 12-core
2009
Mac Pro (Early 2009), Quad-core
Mac Pro (Early 2009), 8-core
Earlier
Mac Pro (8-core)
Mac Pro (Original)
