Half a century ago, the puzzling phrase "special register groups" started showing up in definitions of "CPU", and it is still there. In this blog post, I uncover how special register groups went from an obscure feature in the Honeywell 800 mainframe to appearing in the Washington Post. While researching old computers, I found a strange definition of "Central Processing Unit" that keeps appearing in different sources. From a book reprinted in 2017:1 "Central Processor Unit (CPU)—Part of a compute...