what is the difference between the i3, i5, and i7?
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Speed.  How many sets of instructions can be executed at one time. Number of cores (orbrains) per chip.  Overall though the difference is on such a small scale considering your needs, I think you'll be happy with either of them.  Maybe aim for the Core i5.   I know you work in iPhoto quite a bit. If you were a heavy photoshop user or final cut user then you may be a little more in the market for the i7 but overall I think the middle line would be a great choice. Here’s a great article comparing each.Core i3 vs i5 vs i7: Intel's Processors Explained If you want to get crazy detailed you can check out the Wikipedia page dedicated to the subject here: Intel Core - Wikipedia, the free encyclopedia