This is a terminological confusion. The "computers" you're describing gave their name to the universal symbol manipulators we now call "computers" because, historically, the universal symbol manipulators were originally funded to perform mathematical calculations. They don't have much else in common. The "computers" that Stephenson is talking about are the universal symbol manipulators, the smallest and most limited of which can boot Linux: https://dmitry.gr/?r=05.Projects&proj=35.%20Linux4004