The encyclopedia · Engineering & Operations · Technical decision · 2003-2020s
Amazon stopped sorting warehouse shelves and let software find things
After Harry Potter traffic jams, Amazon abandoned ordered storage for 'random stow', scattering items so space is used, not located.
Amazon
the move
Amazon originally stored books by author surname, the way a bookshop would, so a picker knew where any author's books were. That order made sense to a person, but it meant the warehouse was arranged for browsing rather than for moving goods out fast, and it created hot spots.
The 2003 release of Harry Potter and the Order of the Phoenix broke it. So many orders for one book concentrated in the R section that pickers queued, traffic jammed the aisles, and the first step of delivery slowed. Organizing like a library had created an operational bottleneck.
Amazon threw out the alphabetical scheme and moved to what it calls 'random stow', which it has used in its fulfilment centres for about twenty years. Goods arriving at a receive station are scanned and then stowed in whatever slot is free, deliberately scattered, so a beach towel may sit between batteries and frying pans. Nothing is grouped by type.
The system works because the computer remembers locations. Each shelf and each bin has an identifier, so the warehouse does not need to be ordered for a human to find anything; it needs to be full. Picking becomes a lookup plus a short walk to the slot the system names.
why it works
- Author-surname storage was ordered for browsing but concentrated demand in hot spots
- The Harry Potter release put so many pickers in the R section it jammed the schedule
- Random stow fills free slots, so the warehouse holds more goods per cubic foot
- A lookup in the system replaces a long search down ordered shelves
what transfers
If a machine can look it up instantly, do not spend real estate and walking time keeping things in order; use the space for density and let the index find the item.
what came after
Random stow became the default approach in Amazon's fulfilment network and alongside the robot-driven shelving it helped the company raise storage density and cut picking time. Amazon's own leadership cites the Harry Potter moment as the origin of the re-think; the 'Harry Potter Room' at its Seattle headquarters marks it. The lesson spread across e-commerce and warehouse software, where 'chaotic storage' or 'random slotting' is now a standard term.
references
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