Europe’s ExaNeSt project is putting together a small prototype of what will eventually be a supercomputer with 10 million ARM cores. Why ARM? Because the performance bottleneck in a super is not the CPUs, but the interconnect between them. So it makes sense to use more power-efficient cores to keep the overall cost down. The main cost of running a super, or indeed any massively-multiprocessor installation (data centre, cloud service, render farm etc) is the electricity bill. <http://www.theregister.co.uk/2016/02/02/buddy_can_you_spare_ten_meeelion_arms/>