Other than systems running Linux, there are two Chinese supercomputers running IBM AIX, a Unix variant. This pair, tied at 386 and 387, may not be long for the list. That's because supercomputers are growing ever faster.
Systems running faster than 1 petaflop now occupy the first 117 positions -- nearly a quarter of the TOP500. Last year, there were only 81. At the bottom of the list, the slowest system runs at 349.3 teraflops. In November 2015, the bottom supercomputer ran at 206.3 teraflops.
At 434.8 teraflops, I wouldn't count on the Unix systems being around for another year. If I'm correct, Linux will completely dominate the list by this time 2017.
The fastest supercomputer today, China's Sunway TaihuLight, runs at 93 petaflops. A petaflop is 1,000 teraflops or 1 quadrillion floating-point operations per second.