A New Golden Age for Computer Architecture

We began our Turing Lecture June 4, 201811 with a review of computer architecture since the 1960s. In addition to that review, here, we highlight current challenges and identify future opportunities, projecting another golden age for the field of computer architecture in the next decade, much like the 1980s when we did the research that led to our award, delivering gains in cost, energy, and security, as well as performance. "Those who cannot remember the past are condemned to repeat it."--George Software talks to hardware through a vocabulary called an instruction set architecture (ISA). By the early 1960s, IBM had four incompatible lines of computers, each with its own ISA, software stack, I/O system, and market niche--targeting small business, large business, scientific, and real time, respectively. IBM engineers, including ACM A.M. Turing Award laureate Fred Brooks, Jr., thought they could create a single ISA that would efficiently unify all four of these ISA bases. They needed a technical solution for how computers as inexpensive as those with 8-bit data paths and as fast as those with 64-bit data paths could share a single ISA. The data paths are the "brawn" of the processor in that they perform the arithmetic but are relatively easy to "widen" or "narrow." The greatest challenge for computer designers then and now is the "brains" of the processor--the control hardware. Inspired by software programming, computing pioneer and Turing laureate Maurice Wilkes proposed how to simplify control. Control was specified as a two-dimensional array he called a "control store." Each column of the array corresponded to one control line, each row was a microinstruction, and writing microinstructions was called microprogramming.39 A control store contains an ISA interpreter written using microinstructions, so execution of a conventional instruction takes several microinstructions. The control store was implemented through memory, which was much less costly than logic gates. The table here lists four models of the new System/360 ISA IBM announced April 7, 1964. The data paths vary by a factor of 8, memory capacity by a factor of 16, clock rate by nearly 4, performance by 50, and cost by nearly 6.