The tortoise and the (soft)ware: Moore's law, Amdahl's law, and performance trends for human-machine systems

Human interaction with computing and communication systems involves a mix of parallel and serial processing by the human-computer system. Moore's Law provides an illustration of the fact that the performance of the digital components of any human-computer system has improved rapidly. But what of the performance of those human components? While we humans are amazing information processing machines, our information processing capabilities are relatively fixed. This paper reviews 100 years of the human performance literature and shows, graphically, the disparity between the non-growth in human performance and the geometrical improvements in computational capability. Further, Amdahl's Law demonstrates, algebraically, that increasingly the (non-parallelizable) human performance becomes the determining factor of speed and success in most any human-computer system. Whereas engineered products improve daily, and the amount of information for us to potentially process is growing at an ever quickening pace, the fundamental building blocks of human-information processing (e.g., reaction time, short-term memory capacity) have the same speed and capacity as they did for our grandparents. Or, likely, for the ancient Greeks. This implies much for human-computer interaction design; rather than hoping our users to read or to type faster, we must look for optimally chosen human channels and maximally matched human and machine functions. This tortoise and the (hard-and soft-)ware race demands renewed enthusiasm for, and increased, systematic attention paid to the practice of usability and to research in human-computer interaction.