More cores for everyone – Intel’s new 8th generation CPUs
With the introduction of their 8th generation CPUs, Intel has entered the biggest change to their mobile chips in more than a decade: Four physical CPU cores in processors for thin and light laptops. With software that’s increasingly optimized to make use of more than one or two processor cores, the new CPUs are a welcome change to a range of products which has only seen a slow rate of improvement in the previous years. The new CPUs open new fields of use for small laptops and they may even replace a workstation for some users.
The new 8th generation mobile CPUs are codenamed Kaby Lake-R (Kaby Lake Refresh) and they represent only a slight improvement over previous Kaby Lake processors in terms of architecture and manufacturing process. They also shouldn’t be confused with 8th gen CPUs for desktop systems, which are based on the Coffee Lake architecture. In most aspects, the new 8th gen mobile CPUs are simply two 7th gen mobile CPUs stuck together. With twice the processing cores, parallelized workloads and heavy multitasking enjoy a significant boost in performance, and, since Intel has increased the maximum clock speeds of their CPUs slightly, single threaded workloads also run faster. Under sustained load, however, the difference to workstation CPUs becomes apparent.
Thermal Design Power
Modern CPUs are grouped by the heat they dissipate when running under full load at their base clock speed. The maximum amount of heat is generally defined as TDP, or Thermal Design Power. Previous generations of Neptun devices have used CPUs with 4.5W (e.g. i7-7Y75), 15W (e.g. i7-7500U), or 45W (e.g. i7-7700HQ) TDP. The cooling system of laptops is designed to disperse the heat of the CPU and that of all the other components in the device by the use of heat pipes, cooling fins, fans and other means. Naturally, a CPU with a higher TDP requires a larger and heavier cooling system, which is why thin Ultrabooks aren’t equipped with workstation-grade CPUs. Badly implemented cooling systems may not be able to sufficiently cool a CPU, which causes it to slow down, or they may be very loud, regardless of the TDP of the processor.
Just like their predecessors, the 8th gen mobile CPUs have a TDP of 15W, which means they can be used in the same devices. In theory, however, gluing two 15W CPUs like the i7-7500U together to create its direct successor, the i7-8550U, should result in a TDP that is far too high for thin laptops. That’s where the aforementioned base clock speed comes into play: While the i7-7500U was designed to run at 2.7GHz under sustained load, the i7-8550U only runs at 1.8GHz to stay within the power envelope of 15W. Compare this to a 45W CPU like the i7-7700HQ which can run at 2.8GHz at full throttle and it becomes obvious why hotter CPUs are faster.
The lower base clock speed of the 8th gen CPUs doesn’t mean that they’re slower than their predecessors, of course. Modern CPUs are smart and full of sensors, so they know at which temperature they’re currently running and how many processor cores are needed for a specific workload. For short bursts of activity, the i7-8550U for instance, can increase its clock speed to 4GHz for one or two cores, or to 3.7GHz with all four cores, which is much higher than the 3.5GHz of the i7-7500U. Only once the cooling system can’t keep up with the heat production of the higher clock speeds anymore, the CPU starts to throttle down until it reaches its base clock speed (or lower if the cooling system isn’t adequate). Manufacturers can even design cooling systems that can dissipate more than the minimum required by the TDP, so that a CPU can run at higher clock speeds for a longer time.
The advantage of the new CPUs is heavily dependent on the workload and on how well the manufacturer has implemented the cooling system. Using the benchmark Cinebench R15 as a measuring stick, you can expect up to 80% more performance in a short, multithreaded workload, and up to 15% in singlethreaded workloads, when comparing the new CPUs to their direct predecessors. However, under sustained load the advantage of the new CPUs quickly melts since their cooling solutions reach their limit, limiting the advantages in this synthetic test to still impressive 40% and 10%, respectively. A workstation with a current 45W CPU is still at least 40% faster than the new 15W CPUs in these workloads.
In real-world workloads, the differences aren’t as pronounced, but your system will definitely feel more responsive in general multitasking use. Easily parallelized workloads like rendering, photo editing, and compiling will see significant benefits. Gaming in particular, especially if an external graphics card over Thunderbolt 3 is used, will see significant performance gains, since most modern games use more than two cores and generally don’t put the CPU under full load all the time.
Intel’s new 8th gen mobile CPUs are a welcome upgrade after users of thin laptops have been stuck with two physical cores for more than a decade. All users will be happy about a snappier system, and for some the new processors might even mean that they won’t have to lug around a heavy workstation anymore. Coupled with an external GPU, a light laptop with a new CPU may even replace a gaming laptop. However, for users who need a laptop that can handle high sustained load, a workstation is still the way to go.
The new CPUs are built into most Ultrabooks of the upcoming Neptun Spring Wave and you can check them out first hand at our Demo Days.