We describe the development and key characteristics of the “K computer” supercomputer system, which was developed by RIKEN and Fujitsu as part of an initiative led by Japan's Ministry of Education, Culture, Sports, Science and Technology (MEXT) from 2006–2012. We highlight the technologies used to create the K computer, which is a massively parallel supercomputer system with over 80,000 CPUs and eight cores per CPU. The balance of power consumption, reliability, and efficiency in application performance was the key consideration in the design. The K computer achieved the top performance in the TOP500 ranking in June 2011 (8.16 petaflop/s with 548,352 processor cores) and again in November 2011 (10.51 petaflop/s with 705,024 processor cores), thus breaking the 10 petaflop/s barrier for the first time in the world. The K computer is now operational at the Advanced Institute for Computational Science (AICS) in Kobe, Japan. We also describe the PRIMEHPC FX10, which utilizes enhanced technologies implemented in the K computer, and the future directions we intend to take.