A lot of people assume all i7's have FOUR CORES which is not the case. I forget the differences between mobile i3, i5 and i7 CPU's but all of them have 2-core versions.
You can type in the exact CPU model with the word Intel to Google and can easily find the Intel site link showing the CPU specs including cores, threads (HT), Turbo frequency etc.
is your friend. Regarding the mobile i3, i5, and i7 differences, all of the base models are 2C/4T. An i3 has a small L3 and no turbo mode. The i5 is the same but with a turbo. The i7 has a larger cache and higher freqs, both normal and turbo clocks.
The letter suffix gives a little more info. M is the basic mobile model ( though it looks like they're replacing M with H. ) The U chip is low power and Y is very low power use. These follow the same rules as the M, but the clocks will be much lower and the turbos won't be as high ( the i7 U and Y chips will still have a fairly high turbo. )
Any chip with a "Q" in its name has four physical cores and still adheres to the other general rules. Most i7 chips are also Q models, but not all.