"System" Process High CPU Usage When Idle

[pwx]

I recently noticed that the CPU usage begins to spike due to the "system" process about 5 minutes after the pc is idle (not touching anything), but when I move the mouse, CPU usage returns to normal. I assume that Windows is running something in the background, but I am curious as to what is specifically causing this, since the CPU usage itself is quite odd. On the CPU monitor, only one thread is being used at a time at 100% load (there is never more than one thread spiking up to 100%); I left the task manager open and determined that it was the system process. I just would like to know what is causing this. Two screenshots are attached, one showing the CPU load returning to normal after moving the mouse, and the other showing the task manager displaying the system process cpu usage.

https://postimg.org/gallery/1c4itwgau/

 

[Colif]

That is normal behaviour, windows uses the idle times to run background processes and, as you have noticed, will stop them as soon as you want to use PC. There are things it needs to do like defraging hdd's or index the drives so you can finds things faster. System can also be downloading updates for apps or windows update.

13% usage isn't anything to worry about, especially if it hands it back as soon as you want it.

If you curious, you can download https://technet.microsoft.com/en-us/sysinternals/processexplorer.aspx?f=255&MSPPError=-2147217396 - its a slightly OP version of task manager and its default view (tree) shows the hierarchy and can show you the name of the processes system is running. and then just wait and watch.

this explains the colours: http://www.howtogeek.com/school/sysinternals-pro/lesson2/