I compiled the most interesting answers (in no particular order):
1) OS kernel context-switching
2) Windows System Idle Code: But Some are pointing out that modern version are actually halting the CPU and are used to implement power saving.
3) Graphic processing: GPU code for pixel rendering, codec
4) Network functions. Linux TCP function (which include all Android phone). Others are pointing to the code in Cisco Routers OS processing most of the internet traffic.
5) MPI API (send/recv) (http://en.wikipedia.org/wiki/Message_Passing_Interface)
6) Fast Fourier transformation (FFT) FFT/DFT/DCT processing code.
7) Clock checking code.
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I compiled the most interesting answers (in no particular order):
1) OS kernel context-switching
2) Windows System Idle Code: But Some are pointing out that modern version are actually halting the CPU and are used to implement power saving.
3) Graphic processing: GPU code for pixel rendering, codec
4) Network functions. Linux TCP function (which include all Android phone). Others are pointing to the code in Cisco Routers OS processing most of the internet traffic.
5) MPI API (send/recv) (http://en.wikipedia.org/wiki/Message_Passing_Interface)
6) Fast Fourier transformation (FFT) FFT/DFT/DCT processing code.
7) Clock checking code.
Not sure of the winner.