John Leroy Gustafson (born January 19, 1955) is an American computer scientist and businessman, chiefly known for his work in High Performance Computing (HPC) such as the invention of Gustafson's law, introducing the first commercial computer cluster, measuring with QUIPS, leading the reconstruction of the Atanasoff–Berry computer, inventing the unum number format and computation system, and several awards for computer speedup. Currently he is the Chief Technology Officer at Ceranovo, Inc. He was the Chief Graphics Product Architect and Senior Fellow at AMD from September 2012 until June 2013, and he previously held the positions of Architect of Intel Labs-SC, CEO of Massively Parallel Technologies, Inc. and CTO at ClearSpeed Technology. Gustafson holds applied mathematics degrees from the California Institute of Technology and Iowa State University.