Windows CPU usage is a bit misleading on multi-core systems, i.e. all of them nowadays. It reports TOTAL usage. So if you have, for example, a 4 core system, then "50% usage" means 50% of the CPU's total throughput is being used. That could be either all 4 cores running at half speed, or it could be 2 of those cores running flat out as hard as they can. Warframe tends to do the latter thing: It will typically run 2 threads as hard as possible. If those individual cores running those threads cannot keep up, then the game becomes CPU-bottlenecked even though there are other, unoccupied cores which aren't doing any work.
This is *further* complicated by the fact that modern computers will usually try to move highly demanding threads around to different physical CPU cores, in an effort to spread the heat around. So it runs on core 0 for a little bit, that core gets hot, the operating system moves the thread over to core 2 instead. The problem is that this "hoppin...
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