When Dave Alperson got his first job at an Amazon warehouse in 1997, as a temporary hourly employee, it involved walking around the warehouse with a list of where to find products—mostly books—that customers had ordered. Twenty years later, as a regional director of operations for Amazon in Indiana, he oversees 18 warehouses that barely resemble where he started. Amazon now sells millions of products; each of its 149 warehouses ship tens of thousands of them each day; and those warehouses now look like live-action games of Chutes and Ladders—whizzing with a meticulously coordinated system of conveyor belts, slides, and machines that do everything from attach labels to boxes to check weight for quality control. In the process of building this elaborate system, Amazon has completely redefined warehouse efficiency and customer convenience. Through its Prime membership, it has promised tens of millions of customers free two-day shipping on more than 100 million products, and, last year, it shipped 5 billion items to them. “That was the major innovation,” says Daniel Theobald, who cofounded a warehouse robotics company called Vecna in 1998 and counts major retailers and logistics companies as clients. “As soon as people realized, you can order something and get it tomorrow, that turned the industry upside down.” The core of this disruptive efficiency, though, is not Amazon’s automated shelf-moving warehouse robots, which is the innovation that gets the most attention. And it isn’t, on its surface, something that you would associate with a well-oiled machine. It’s not even a breakthrough technology. In fact, some version of it was already in place when Alperson worked in Amazon’s early warehouses. Read more at Quartz.