The faster one is called Core i7 3689Y and has two cores and two threads, as well as a base clock of 1.5GHz. With the help of Intel Turbo Boost 2.0, the top single-core turbo clock is an impressive 2.6GHz, while the maximum dual-core turbo clock stops at 2.4GHz, which is still impressive. This core comes with Intel HD graphics 4000 clocked between 350MHz and 860MHz with turbo.
This new core supports both DDR3 and DDR3L at 1600MHz, has 4MB of cache and impressively low 13W TDP. We have explained that SDP stands for Standard Dissipation Power and Intel expect it to be at 7W for this part.
The runner up is called Core i5 3439Y and has the same two cores and two threads with 1.5GHz base clock, but the single core turbo clock stops at 2.3GHz, while the dual-core top clock is 2.10GHz. The graphics speed, TDP and memory support remain the same, but there is a difference in cache size. Core i5 3439Y comes with 3MB instead of 4MB for Core i7 Y series 3689Y part.
The Haswell version of Y part won’t be coming at least until Q3 2013, if not even later, which implies that it takes some extra optimizing to take that TDP from U series 17W down to 13W necessary for Y line.