Jim Keller is a microprocessor engineer best known for his work at AMD and Apple. He was the lead architect of the AMD K8 microarchitecture (including the original Athlon 64) and was involved in designing the Athlon (K7) and Apple A4/A5 processors. He was also the coauthor of the specifications for the x86-64 instruction set and HyperTransport interconnect. From 2012 to 2015, he returned to AMD to work on the AMD K12 and Zen microarchitectures.