The significant gain in performance between Kaby Lake and Kaby Lake-R U-series parts, with a 15W TDP, is all down to two factors: double the amount of cores and threads, along with higher boost frequencies. It’s remarkable that Intel has been able to make this upgrade without harnessing a new process node or architecture, but I’m glad they have. The result is the largest year-on-year improvement to ultraportable CPU performance in quite some time.
Despite the same TDP between the Core i7-8550U we looked at here and last year’s Core i7-7500U, there are times when the 8550U fully utilizes the additional two cores at the maximum boost frequency to provide more than double the performance. This sort of performance may only be experienced with relatively short workloads, but it’s impressive nonetheless, especially as many laptop-typical loads are short in duration. If these loads utilize all four cores, expect to see huge improvements. While you won’t see as good performance across the board, the gain from Kaby Lake to Kaby Lake-R is still enormous in multi-threaded situations. Video rendering was 40 to 50 percent faster, while MATLAB simulations were 30 percent faster. Even physics workloads in 3D games benefit from the additional CPU horsepower, to the tune of 50 percent in 3DMark Time Spy. Across every workload, on average we saw the i7-8850U outperform the i7-7500U by 49 percent. That’s huge.
Single-threaded performance gains are naturally a lot lower, and dominated by Kaby Lake-R’s higher Turbo frequencies for single-core loads. We saw gains typically around the 10 to 15 percent mark, though this can be as high as 30 percent, which is nothing to snuff at for a generational upgrade. However, most of the performance gains do come in multi-threaded workloads, which are reasonably abundant in 2017. These CPU speed gains allow the i7-8550U to come remarkably close to the performance of the 45W i7-7700HQ, although the 7700HQ does still hold a respectable advantage in sustained workloads. Previously, the 7700HQ was more than twice as fast as Intel’s U-series parts; now, the gap is more like 30 to 40 percent.
If you’re upgrading from an older laptop with a 5th-generation Core i7 Broadwell processor, for example, you can expect to see gains in the order of 70 percent during multi-threaded workloads, and potentially up to double the performance if you’re upgrading from a Core i5.
One thing we haven’t discussed in this review is power consumption. This is fairly tricky to evaluate on a laptop platform, as battery sizes vary significantly between each product. However, our experience using the Dell Inspiron 13 7000 2-in-1 has been very solid in a general sense, despite the laptop only having a 38 Wh battery (smaller than average for an ultraportable). At the very least, it seems that Kaby Lake-R battery life is no worse than Kaby Lake for this type of configuration, despite the increased performance. As we review a range of Kaby Lake-R laptops in the coming months, how the new line of processors stacks up in terms of efficiency will be revealed. For now, what we can say is that Kaby Lake-R and the Core i7-8550U provides a huge improvement in performance over its predecessors. If you were holding off buying a new laptop because performance gains in the last few generations have been disappointing, now might be the time to make a move. Cons: Not a significant architectural upgrade from Kaby Lake.
