CPUs multiply power by adding cores. Each core added increases processing power of data by the amount of a single core.
What Quad-Core Means
Quad-core signifies that a specific CPU has four cores in it. It is like a processor with four little processors inside it that either share one cache efficiently or have a dedicated one for each to provide four times the processing power of a CPU with only one core of the same kind.
A quad core processor gives you the benefit of being able to manage a lot of things in one shot. Multitasking is much easier when the processor has more than one core working at any given time.
Unfortunately, the evolution of processing technology slows down gradually because of limitations in concentrating a large amount of transistors in a small amount of space. Such a concentration causes a large amount of electrical impedance to build up in the electric circuits of the processor and overheats it.
Besides how many cores a processor has, you should also look at other things, such as the front side bus (FSB) speed, which affects how quickly it communicates with peripherals in the computer. You should also pay attention to the architecture of the processor. (Nehalem processors, for example, are much more efficient than Penryn processors.)
In addition to the simple features of a processor, such as clock speed, there are other things affecting its performance, such as how it handles multiprocess or multithreaded environments in an operating system. A great example of a technology processors use to efficiently handle multitasking is known as hyperthreading, which allows processor resources to be used more efficiently.