I just got a new Apple MacBook Pro 13", mid-2012, which has a dual-core Intel i5 Ivy Bridge CPU. When I run Activity Monitor and turn on the Floating CPU Window, it shows a 4-bar graph (indicating 4 cores).
On my older MacBook Pro with an Intel Core 2 Duo dual-core processor, Activity Monitor only showed a 2-bar graph (indicating 2 cores).
Why does Activity Monitor seem to indicate that my Mac has 4 cores, when clearly it does not?