Difference Between Dual Core And Quad Core

I wanted to know what the difference is between dual core, dual core 2 duo and quad core. Between the dual core and dual core 2 duo I know there is a major price difference, the dual core 2 dual being the costliest.
But the details which I would like to know is the specifications of each and how they differ.
Dual core - It is just a entry level cpu with two cores
Core 2 Duo - Far more superior than Dual core and cache memory gets increased
Core 2 Quad - it has 4 cores and it is one of the costliest i guess

Basically if you got heavy usage you should go with core 2 quad it got 4 cores and all the latest applications support quad cores and performance gets improved.
If you are looking forward to buy any of these don't go with dual cores and core 2 duo or if you can afford latest gen processors that would be great.

Core 2 Quad being superior in the above mentioned list by you. It still beats 1st and 2nd gen i3.
A dual core is a processor which has two execution cores and a quad core is a processor which has four execution cores. This is the main difference between the two. Unfortunately I don't know the difference in the dual core duo 2.
The dual core and dual core 2 duo dont have much of a difference, the 2 duo is an updated version of the dual core but the quad core has two dual core processors and therefore is much faster.