> For context, on newer CPUs such as on Skylake and beyond, Intel has refined the instructions used to disable branch speculation to be more specific to indirect branches, reducing the overall performance penalty of the Spectre mitigation. Older versions of Windows have a larger performance impact because Windows 7 and Windows 8 have more user-kernel transitions because of legacy design decisions, such as all font rendering taking place in the kernel. We will publish data on benchmark performance in the weeks ahead.
Source: https://cloudblogs.microsoft.com/microsoftsecure/2018/01/09/...
An article in the verge states "Windows 7 and Windows 8 will be the worst hit simply because these older operating systems have features like kernel-level font rendering that will be impacted by the Spectre and Meltdown mitigations even further than Windows 10."
> Older versions of Windows have a larger performance impact because Windows 7 and Windows 8 have more user-kernel transitions because of legacy design decisions, such as all font rendering taking place in the kernel. We will publish data on benchmark performance in the weeks ahead.
In other words: If the fix would cause Windows 7 to lose X% performance, Windows 10 would lose that same X% plus any Y% advantage it had over Windows 7.
(This is just a guess, of course.)
> Windows 10 PCs with Haswell or older processors will see "more significant slowdowns" and Microsoft notes that a segment of customers may "notice a decrease in system performance”. > Windows 7 and Windows 8 PCs powered by Haswell or older processors will see a "decrease in system performance" for "most users".
Does it mean that if you care about performance, it's better to use Windows 7 instead of 10? It's not spelled out explicitly, but they way they worded it suggests so.