Like with other companies, Microsoft's Spectre and Meltdown security fixes introduced a performance hit -- it mostly affected servers, but it was there. Thankfully, that blow shouldn't be quite so severe in the next several months. The company's Mehmet Iyigun has confirmed that a major Windows 10 update in the first half of 2019 will use Google's Retpoline solution to mitigate Spectre version 2 attacks without the usual slowdown. The improvement should be such that the impact will be "noise-level" in most situations. You may not even notice, then.