The Intel® Core™ 2 Duo is a dual core processor, but not all Dual Core processors are Intel Core 2 Duos. In the end we would need to know the models of the processors you are asking about in order to give you a better answer.
I am going to assume vickyjaju is referring to the Pentium Dual-Core CPU series which is based on the Allendale / Wolfdale cores used in the Core 2 Duo series.
The Pentium Dual-Core CPUs are slower than Core 2 Duo CPUs because they use slower RAM. The Allendale Pentium Dual-Core CPUs uses DDR2-400 RAM, Allendale Core 2 Duo CPUs uses DDR2-533 RAM. Wolfdale Pentium Dual-Core CPUs can use up to DDR2-533 RAM, while Woldale Core 2 Duo CPUs can use up to DDR2-667 RAM.
There is also a difference in the L2 cache. The Allendale Pentium Dual-Core CPUs has 1MB of L2 cache, Allendale Core 2 Duo CPUs has 2MB or 4MB of L2 cache pending on the model. Wolfdale Pentium Dual-Core CPUs also have 2MB of L2 cache, while Woldale Core 2 Duo CPUs have 3MB or 6MB of L2 cache depending on the model.
Overall, Pentium Dual-Core CPUs are probably around 5% to at most 10% slower than Core 2 Duo CPUs.
core 2 duo but if you're making a new build get something better. You can get a 6 core AMD processor for $150. Dual cores are dying, I wouldnt jump on the dual core train at this point. Althought, if it is just for a simple build for surfing the internet or whatever go for an I3.
according to your question? the term "core 2 duo vs dual core" are same in cores and thread but core 2 duo are newer and latest than dual core, for example core 2 duo have 2 physical cores and 2 threads similar dual core also have 2 cores and 2 threads but?
dual core have low speed frequency overclocking not good low cache memory can't handle gfx card old architecture with 65nm lithography which is pretty bad, on the other hand core 2 duo have good speed great overclocking better cache memory like 6mb or 4mb can handle high end video cards latest architecture with 45 nm.