为什么英特尔命名 i 系列 CPU 是 i3、i5、i7 呢？为什么不是 i3、i4、i5 ？

The information on letters and numbers is not longer corresponding to a specific technical features or technology on the Products.
This naming scheme is now divided as low-level units (Core i3), mid-range units (Core i5) and high-end performance processors (Core i7).

These names were selected only for marketing purposes.

http://communities.intel.com/thread/28871