So I've been using this site, Moon Bitcoin for a little while (it's a faucet), and recently they have added a feature to do some bitcoin mining in the background, to increase the amount of bitcoin you get to claim. Today, I turned it on, and set it to "very high CPU usage", and sure enough, my processor immediately shot up to 100%. I don't have a powerful computer, I have a Pentium N3700 in my laptop, with integrated graphics. While that mining process was running, I unpaused a YouTube video I was watching, expecting it to lag (when I run a CPU intensive application, or game, YouTube lags). To my surprise though, it played like normal, really smoothly, even normal usage seemed really smooth. My question is, how is my computer running so smoothly, even with 100% CPU usage in task manager?
The CPU usage just tells you how busy the CPU is. It does not tell you whether some processes would like more CPU time but cannot get it. In Linux/UNIX environments, this is measured using the “load average”. You cannot tell whether your PC is overloaded just by looking at the CPU usage.
The mining process is most likely running at a very low priority. This means that it’ll get less CPU time as processes with higher priority use more. On the same priority level, processes have equal weight. Scheduling is a very complex topic.