Apart form the new 14 nm architecture (4th gen was 22nm) the major difference we'll see is in mobile computation. Intel instead of manufacturing 'U' series processors separately for tablets and laptops they decides to manufacture a whole new architecture that would consume less power because of its 14nm dye gap without compromising on performance as used to happen in 'U' series processors of the equivalent desktop model. As per the intel's data sheet " The 5th Generation Intel Core (U series) processors utilise Intel’s new 14nm process technology to improve upon the previous generation Intel Core processor’s success with 35 percent more transistors on a 37 percent smaller dye. The new process, combined with architectural enhancements, enables the 5th Generation Intel Core processors to deliver up to 24 percent better graphics performance, up to 50 percent faster video conversion and battery life that is up to 1.5 hours longer ". Consumers who are planning to refresh a 4-5-year-old PC will also notice significant improvements: graphics performance up to 12 times better, video conversion speed up to 8 times faster, productivity performance up to 2.5 times faster, wake times 9 times faster, all with up to 2 times longer battery life. So its better for mobile devices to use these 5th gen processors over same U series 4th gen processors... as think is that processors to great relational of computer.