duel core mean two processors in one and x3 mean three and so on so olny a single will have one processor.
'Dual Core' is a generic term for processors with two cores. Core 2 Duo is a dual core processor brand designed by Intel.
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The major difference is that an Intel Core processor is 32-bit, while Intel Core 2 processors support 64-bit operation. At the same clock speed, L2 cache, and FSB, they will perform about the same.
To be blunt, the Core 2 duo has two proccesing cores while Core 2 quad has four proccessing cores.