The June 2015 F500 Top Ten Supercomputers
Of note: the top of the list has basically remained unchanged for some time.
While in first place there is an Intel Xeon system. But in second place, and not new to the place in the list, is an AMD Opteron based system.
Also, of the top ten machines, 50% are AMD64 architecture and 50% are RISC based architecture.
Of the RISC machines, 80% are IBM POWER architecture and 20% are Oracle Sparc architecture.