IBM PowerXCell 8i

The first accelerator to put a machine at the top of the list, and a design borrowed almost intact from a games console: the Cell in Roadrunner is the PlayStation 3 processor with double precision fixed. That is the pattern that has governed this market ever since. Accelerators are affordable in supercomputers because a far larger consumer or enterprise market has already paid for the design, and the eight synergistic processing elements had software-managed local stores rather than caches, so the programmer moved every byte by hand. Roadrunner was famously difficult to program, IBM cancelled the line, and the industry took the idea to NVIDIA instead.