Amazingly, ordinary warehousing systems use up only about 40% of the total available space for storage of materials or goods, the rest is allocated for aisles. Stacking up the cartons, bags or crates of the materials in their maximum heights does not alleviate much the wastage of space. This may be tolerable when there is less materials to store, but when space is at a premium, solutions have been ordinarily found through pallet racking or building storage mezzanines. Like the concept of skyscrapers that use up little ground area but much of it upwards, vertical storage has been an adequate solution, at least until lately.

Mobile storage. The twin overriding problems of storage management have always been storage space and materials access. Vertical storage uses the available space above ground level, commonly empty in most conventional warehousing methods. However, there is still the mostly unused 'road system' for accessing and retrieving materials, the aisles. The warehouse forklift can only use its own space at any one time, so that the aisle spaces it is not on is wasted.

The mobile storage concept moves the racks together if the aisle between them is not in use so that the space is not wasted. The appropriate racks are then moved apart when needed to allow the forklift access to the materials. In this way the space between racks or shelves are used, granting as much as 100% additional storage space. The racks or shelves are moved either manually or with mechanical assistance.

Vertical carousels. Similar in concept to the restaurant dumbwaiter or the Rolodex, vertical carousels add storage space by minimizing the need for mechanical transporters like a forklift. Since the materials are placed in bins, racks or shelves readily retrievable by humans, the aisle space between the carousels may be reduced, opening up additional space for storage. One advantage of this concept is that the materials are always accessed at the same height level, which can be a boon for the retrieving persons. However, vertical carousels are mostly used for small-sized materials.

Automated self-storage. This one is run by computer and eliminates the need for human intervention, at least most of the time. While the materials are stored in uniform-sized modules and stacked in racks and pallets, loading and retrieval is performed by an automated loading-retrieval forklift-like machine that takes the appropriate module to the person at the retrieval window. The same machine accepts the modules from the loading window for storage. So in effect the machine is the warehouseman with the human as the supervisor.

As space gets scarcer for storing materials in a manufacturing or selling enterprise, the search for solutions continues at an ever increasing rate. The first general solution direction of vertical storage has been followed by mobile storage, both lateral and vertical, seemingly using up the options so that so far no new directions are readily foreseen. However, the search has not ended and no doubt we will see more revolutionary solutions in the future, short of shrinking the materials themselves.