The microprocessor revolution, of which this issue marks the 50th anniversary, drove remarkable innovations in instruction set architecture, microarchitecture, and system design, some of which continue to evolve in current research and commercial products. Many of these features were indeed new, but others have their roots in a line of processor architectures that predates this revolution and that, alone among those ancient species, continues to thrive in modern information technology (IT) world: the IBM mainframe, launched in 1964 as S/360 and now continuing as IBM Z. This article will briefly describe some of the “modern” features that were pioneered there, then recount how the mainframe made the transition into the complementary metal–oxide–semiconductor (CMOS) microprocessor world.