That&#x27;s a old manual Amazon facility. The newer ones use Kiva robots to bring the shelving units to the pickers, rather than the pickers going to the shelving units.<p>The manual system isn&#x27;t that different from the Sears &quot;schedule system&quot; introduced in 1908.[1] Note the line &quot;pickers don&#x27;t necessarily pick items for a single or even complete order.&quot;  That&#x27;s crucial.  Orders are split apart and combined pick lists generated. Picked items then flow towards order assembly stations, which Amazon calls &quot;sort&quot;. At any one time, some maximum number of orders are in progress, limited by the number of output boxes at order assembly.  Amazon does this with computers; Sears did it with clerks and pick slips, with Sears giving each order an assembly bin for a fixed number of minutes.<p>Separating picking from order assembly and inserting a sort phase reduces the order of the problem.  Picking N orders from M items individually means O(N × M) cost, because as inventory becomes larger, the pickers travel more distance.  With separate picking and assembly, performance is something like O(log(M) × N) cost, because each picker works in a limited area.  That was Sears&#x27; big breakthrough.<p>[1] <a href="https:&#x2F;&#x2F;news.google.com&#x2F;newspapers?nid=1734&amp;dat=19721006&amp;id=bXkcAAAAIBAJ&amp;sjid=AVIEAAAAIBAJ&amp;pg=3170,3159101&amp;hl=en" rel="nofollow">https:&#x2F;&#x2F;news.google.com&#x2F;newspapers?nid=1734&amp;dat=19721006&amp;id=...</a>