Blame Kaby Lake’s Speed Shift and Zen’s SMT for Windows 10 Restrictions
Microsoft recently announced that they will support the next generation Intel Kaby Lake and AMD Zen CPU architectures only on the latest Windows 10. This sparked an uproar and caused plenty of confusion which is quite understandable. Windows 7 is still the second most popular desktop OS among enthusiasts, while amount of users running Windows 8.1 can’t be ignored as well.
So Microsoft not supporting older OSes will leave a lot of consumers with only a fewer options when it comes to processors. This created a general perception that the decision could be a pure marketing move by Microsoft to force users to upgrade to the newest operating system. But it seems like that might not be the case.
HotHardware has just dug into the matter to find out what could be the possible reasons for Microsoft to limit support for the new CPU microarchitectures to Windows 10. It appears that new power-management and SMT features are the real culprit.
We know that Intel’s Kaby Lake comes with a new feature called Speed Shift Technology. This is designed to allow the processor to adjust its clock speed according to processing loads at a 15 ms response time. Speed Shift is enabled in hardware, but OS-level hooks are also required for proper functioning, which means the on-die power-management components can poll for processing loads.
We have a similar case with Zen microarchitecture, which according to AMD features a fine-grained, multi-domain clock-gating throughout the chip. Zen-based processors also sport simultaneous multi-threading (SMT) which makes the CPU design much closer to Intel’ in that each physical core now appears as two logical CPUs to the OS. This will help better utilize on-die execution resources and improve core instructions per clock.
To properly leverage SMT on Zen, Microsoft will have to update OS kernel and system scheduler–something they did with Windows 7 to optimize it for Bulldozer.
It’s worth mentioning that Microsoft used the word “support” and not “compatibility” for next-gen CPU architectures from AMD and Intel. This means Windows 7 and 8 won’t suddenly stop working on the new Kaby Lake and Zen based processors, but they are not going to receive future updates and optimizations that would be exclusive to Windows 10.