While ten cores may seem an overkill, the 20nm Helio X20 is actually more about its "Tri-Cluster" architecture that consists of two 2.5GHz Cortex-A72 cores, four 2GHz Cortex-A53 cores and four 1.4GHz Cortex-A53 cores. So basically, on the CPU side the Helio X20 is very much a Helio X10 with two more Cortex-A72 cores, but with the original eight Cortex-A53 cores running on slightly lower speeds.
Finbarr Moynihan, MediaTek's General Manager of International Corporate Sales, analogized the addition of a third CPU cluster to having an extra gear in a car, in order to improve its fuel efficiency across different terrains. In other words, there's no longer a sudden jump from the low-power cluster to its high-power counterpart, so you get a better overall curve across the power-performance spectrum. This also allows the low-power cluster to go even lower in terms of power required, and the high-power one to be even more powerful -- hence the use of Cortex-A72 instead of yet more Cortex-A53 cores.
So here comes the classic question: Can all ten cores run simultaneously? Moynihan says while that's allowed, the chip's software will always pick the ideal clusters to handle different threads. For instance, mail apps and simple messaging apps can run on the low-power cluster, whereas casual games and multimedia apps can make do with the middle cluster, thus leaving the high-power cluster to resource-intensive games and other heavy duty apps. Statistically speaking, you won't often see all ten cores operating at the same time.
"I think it's much more likely that it will be a subset of the ten cores but in different configurations, depending on the load that might be on at the same time," the exec added. "In theory, the scheduler can turn on all ten [cores] if necessary; of course, subject to any thermal constraints that the device may have."
Compared to its predecessor, the more premium Helio X20 also benefits from the additional integrated Cortex-M4 hub (for low-power sensors and low-power MP3 playback), dual 12-bit camera processors, improved graphics performance yet lower power requirement on that plus the modem, as well as Carrier Aggregation for the faster Cat 6 LTE -- a feature that Moynihan admitted the Helio X10 often gets criticized for excluding.
"Adding the next-generation modem and the Carrier Aggregation feature specifically, I think, makes this platform relevant on a much more global scale for higher tier and even flagship devices."
Ultimately, we'll need to see how well can the Helio X20 handle its clusters, as well as how efficient the new integrated modem is in real life. The bad news is we won't get to do so until early 2016 the soonest, but the good news is MediaTek and device manufacturers have almost half a year to fine tune the chip's performance, so time will tell.