A system, comprising: an inventory station comprising: a processing location; and a queue having at least a first row and a second row; a first group of physically connected inventory holders comprising the first row of the queue, wherein a first inventory holder in the first group is located at the processing location; a second group of physically connected inventory holders comprising the second row of the queue; and a first mobile drive unit operable to: dock with one of the inventory holders in the first group of physically connected inventory holders; after a first inventory holder is processed at the inventory station, move the first group of physically connected inventory holders such that a second inventory holder in the first group of physically connected inventory holders is moved to the processing location; cause the first inventory holder to disconnect from the first group of inventory holders, wherein the first inventory holder is transported from the queue to a storage location; and a second mobile drive unit operable to: dock with a third inventory holder in the second group of physically connected inventory holders; and after the first group of connected inventory holders is processed at the processing location, move the second group of physically connected inventory holders to the first row of the queue while docked with the third inventory holder. an inventory station comprising: a processing location; and a queue having at least a first row and a second row; a processing location; and a queue having at least a first row and a second row; a first group of physically connected inventory holders comprising the first row of the queue, wherein a first inventory holder in the first group is located at the processing location; a second group of physically connected inventory holders comprising the second row of the queue; and a first mobile drive unit operable to: dock with one of the inventory holders in the first group of physically connected inventory holders; after a first inventory holder is processed at the inventory station, move the first group of physically connected inventory holders such that a second inventory holder in the first group of physically connected inventory holders is moved to the processing location; cause the first inventory holder to disconnect from the first group of inventory holders, wherein the first inventory holder is transported from the queue to a storage location; and dock with one of the inventory holders in the first group of physically connected inventory holders; after a first inventory holder is processed at the inventory station, move the first group of physically connected inventory holders such that a second inventory holder in the first group of physically connected inventory holders is moved to the processing location; cause the first inventory holder to disconnect from the first group of inventory holders, wherein the first inventory holder is transported from the queue to a storage location; and a second mobile drive unit operable to: dock with a third inventory holder in the second group of physically connected inventory holders; and after the first group of connected inventory holders is processed at the processing location, move the second group of physically connected inventory holders to the first row of the queue while docked with the third inventory holder. dock with a third inventory holder in the second group of physically connected inventory holders; and after the first group of connected inventory holders is processed at the processing location, move the second group of physically connected inventory holders to the first row of the queue while docked with the third inventory holder.