Core 2 Quad is a true 4 core CPU, the Core i3 is a dual core processor that is hyper-threaded, so it can run 4 threads at a time. In my opinion, the price of the i3's makes them pretty much worthless because you can get a true quad core CPU for much less from AMD. If you need a budget CPU to upgrade a socket 775, get the C2Q, but if you are building a new system, get an i5 750 quad core if your budget allows, but if you can't spend that much, get an AMD quad core for much less (2.8-2.9 GHz AthlonII x4's are only $100-$110!).