Dual core processors are those that contain 2 cores in a single silicon chip while Core 2 Duo is the name given by Intel to its second batch of dual core processors.

The processor wars have hit a major speed bump as clock speeds become harder and harder to push upwards. Because the number of transistors in a single chip continues to follow its upward trend, processor manufacturers like Intel and AMD have decided to go a different route in increasing the performance of their products, adding more cores into a single chip that leads to a performance boost if the OS supports it. Two or more cores can greatly aid in multi-tasking where each core can work independently of each other. All processors that have 2 cores in them are collectively called as dual core processors regardless of which manufacturer it came from, while those that have 4 processors in a single chip are called quad core.

Initially, Intel called their dual core processors as Core Duo, a very obvious reference to two cores, while AMD called theirs the X2. Intel’s dual core processors were simply 2 Pentium 3 processors that were fabricated in a single chip. As they refined their product more, they decided to differentiate their second set of processors from the Core Duo and decided to call it Core 2 Duo.

Basically, the difference between dual core processors and the Core 2 Duo processors is just in the semantics as Core 2 Duo is simply a name given to a more recent family of dual core processors. If we translate this to the single core processors, we can say that Core Duo is Pentium 1 while Core 2 Duo is Pentium 2, while AMD has their own processors with different names; but all these are still single core processors. We can therefore say that Core 2 Duo is simply a subset of all the dual core processors that are out in the market today.

A complete overview of all Intel processors is given at:
http://en.wikipedia.org/wiki/List_of_Intel_Core_microprocessors

A full comparison of the different Intel Mobile processors in more detail is given at :
http://www.intel.com/support/processors/mobile/pm/sb/CS-007967.htm

Summary:
1. Dual core is the generic name given to processors that have 2 cores on the same chip
2. Core 2 Duo is the second line of dual core processors from Intel
3. Other dual core processors aside from Core 2 Duo are the Core Duo from Intel and the X2 series from AMD
4. All Core 2 Duo processors are dual core but not all dual core processors are Core 2 Duo