Microsoft has run some benchmarks on the Meltdown and Spectre memory vulnerabilitie, and it's unfortunately bad news if your system is a few years old. While the patches for Meltdown and one variant of Spectre will have a "minimal performance impact," fixing a second Spectre variant through low-level microcode imposes a tangible speed penalty and it's particularly bad on systems released around 2015 or earlier. If you have a PC with a 6th-generation Intel Core processor or later, you should only see a hit in the "single-digit" percentage range. That's small enough that you might not notice a thing. If you're using a 4th-generation Core or older CPU, however, you'll see "more significant slowdowns," some of which could be noticeable. And that's if you're using Windows 10. Most Windows 7 or 8 users on similar hardware should notice the effect, while Windows Server is bound to take a more substantial performance blow due to its heavy dependence on I/O.