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More cores are in theory more efficient because they allow for an increase in processing power without the same increase in power requirements that would be necessary from a faster clock speed. So, for example, a 1.5Ghz dual core CPU may offer performance equal to a 2.0Ghz single core CPU, but with lower power requirement and less heat generation. This is particularly important in tablet and smartphone design. Note that the 1.5/2.0Ghz numbers are just an example I made up off the top of my head, so that particular comparison may not be accurate. However, unless both the OS and software make use of the multi core architecture, you will not really see a benefit.