The performance of the systems on the Top500 list continues to improve exponentially. (Note that it's a logarithmic scale on the vertical axis, with each line marking a tenfold improvement.) The three series of dots here represent the total performance of the top 500 systems at the top, the performance of the No. 1 system in the middle, and the performance of the 500th system at the bottom.
The system design of the Top500 supercomputers has changed over the years. In the 1990s, symmetric multiprocessor (SMP) and massively parallel processing (MPP) systems dominated, but now most systems are clusters, which use a looser interconnection among server nodes than MPP machines. (Note: the vertical access is the percent of the Top500.)
Supercomputers these days are getting a speed boost from special purpose helper processors called accelerators. Nvidia's graphics processing unit (GPU) chips, repurposed to perform numeric computations, are the most common.