Kiva's system can adapt in other ways as well. If someone orders red pens that happen to be stored on the top shelf of a shelving unit, the system software directs that unit to a tall worker who can easily reach the pens. If red pens become hot sellers, the system will instruct stockers to stop putting them on the top shelf and start putting them on the middle shelf, where everyone can reach them. Also, the "peanut-butter and jelly algorithm," as Mountz calls it, tells stockers to place items that are frequently bought at the same time on the same shelf. This can be changed as demand shifts from day to day, or between the summer and Christmas. Around Christmastime, the system can also direct robots to stations with the appropriate style of wrapping paper.

For Walgreens, the software will need to keep track of another parameter: expiration dates. It will ensure that items that can go bad, such as certain cosmetics, are sent out in the order that they're stocked. (Walgreens will use the system to supply its store, not to fill orders from consumers.)

Kiva's adaptive software is the key to the system. The hardware isn't remarkable. The robots are small, wheeled boxes short enough to slip under a shelving unit and lift it up. The navigation system is simple, involving stickers on the floor, optical sensors, and Wi-Fi connections. The software prevents the robots from running into each other, and it keeps track of products on the ever-changing warehouse floor. Infrared sensors warn the robots of unexpected objects in their path--such as a box or a broken robot. Algorithms then kick in to reroute robots around the obstacle. The shelves themselves have lights that tell workers where to stock items, or where to find them in order to pack them. Bar-code scanners register when workers have packed an item and signal the next robot to move into position.

Kiva engineers are working on ways to improve the system. Right now, if a robot breaks down and maintenance workers need to go out on the floor to retrieve it, they virtually "rope off" the area in the warehouse, telling the software to route robots around the area. Mountz says that the engineers are developing a wireless device they call the Moses badge that will allow workers to walk safely among the shelves. The badge will signal the mass of robots to part and allow the workers through.

Rodney Brooks, professor of robotics at MIT, says that the Kiva system is a "very interesting" application of robotics. "It is increasing the productivity of people by having robots do the easy tasks and letting people do the hard tasks," he says. "At the moment, it is incredibly hard for robots to manipulate varying objects. So Kiva leaves that to people and lets the robots do the relatively easy task of moving something from one place to another." Eventually, Brooks says, robots may be able to handle all the tasks involved: "Don't expect the current hard tasks for robots to stay hard forever."