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Automated Storage and Retrieval Systems: 7 Types and Trade-offs
Automated storage and retrieval systems (AS/RS) explained: how they work, the 7 main types, when an AS/RS pays off, and when another option fits better.
6 min read
· Updated
November 2026
At a glance
The definition
An automated storage and retrieval system (AS/RS) is a computer-controlled system that automatically places loads into set storage locations and retrieves them on demand, from pallet cranes to robotic grids.
When it pays off
Dense storage in costly or constrained space, high and steady order volume, a long planning horizon, and harsh areas like freezers where fewer people should work.
The trade-offs
High upfront cost, long lead times, throughput capped by machines and ports, and less room to change when your items, volumes, or building change.
Automated storage and retrieval systems (AS/RS) are computer-controlled systems that automatically place loads into set storage locations and retrieve them on demand, using cranes, shuttles, carousels, lifts, or robots. Common types range from pallet cranes and mini-loads to shuttles, carousels, vertical lift modules, and robotic cube storage.
When you run out of floor space, the usual options are a new building, an overflow site, or going up. An AS/RS is the most automated way to go up: it stores inventory densely, often higher than people can safely reach, and brings each load to a workstation when an order needs it. That trade works well when space is expensive and volume is steady. It gets costly when your business changes faster than the system can.
This guide covers how an AS/RS works, the main types, when it pays off, the trade-offs, and the alternatives. For the full menu of systems, see the warehouse automation guide.
How an AS/RS works
MHI's AS/RS industry group defines an AS/RS as a combination of equipment and controls that handles, stores, and retrieves materials with precision, accuracy, and speed under a defined degree of automation. In practice, every AS/RS has 4 parts:
Storage structure. Rack, shelving, trays, or a grid built for the system, usually taller and denser than conventional racking.
Retrieval machine. A crane, shuttle, carousel drive, lift, or robot that moves loads in and out of storage.
Pick or transfer stations. Ports where people or robot arms pick from the delivered load, or where pallets transfer to conveyors or vehicles.
Controls and software. Software that tracks every location, sequences requests, and connects to your WMS or warehouse execution system.
Throughput depends on the number of retrieval machines and ports and on how well requests are sequenced, not on how fast people walk. Because the system brings each load to a port, many mini-load, shuttle, carousel, VLM, and cube systems double as goods-to-person picking systems.
Types of automated storage and retrieval systems
Unit-load AS/RS. Machines store and retrieve large loads, usually 1,000 pounds or more and typically on pallets, in rack structures that can reach 100 feet tall or more. Best for high pallet counts and full-pallet moves.
Mini-load AS/RS. The same idea for lighter loads, usually under 1,000 pounds, in totes, trays, or cartons.
Shuttle systems. Shuttles automate the handling of totes, trays, and cartons within the rack, in warehousing or manufacturing.
Horizontal carousels. Bins rotate on a horizontal track to bring the right bin to the operator, suited to small parts and pieces.
Vertical carousels. Shelves or carriers rotate vertically, like a Ferris wheel, to provide high-density storage.
Vertical lift modules (VLMs). Trays are stored in columns at the front and back, with an automatic inserter/extractor in the center that stores and retrieves the required trays.
Cube-based storage. Robots store and retrieve bins from a dense cubic grid and deliver them to ports for piece picking.
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When an AS/RS pays off
Space is the constraint. Land or rent is expensive, the building is full, or you can't expand. An AS/RS uses height and narrows or removes aisles.
Volume is high and steady. The system runs many hours a day, most days of the year, on a predictable item profile.
Items fit the containers. Most SKUs fit standard totes, trays, or pallets within the system's size and weight limits.
You plan to stay. You own the building or hold a long lease and expect the operation to run for years.
Security or environment matters. You need controlled access to high-value items, or you run freezers and other harsh environments that can be hazardous to people.
MHI's industry group says AS/RS can save "up to 85%+" of otherwise wasted floor space, increase labor productivity by up to 85%, and raise accuracy to 99.99% or higher. Treat those as supplier-side upper bounds, not a forecast for your site, and model your own case with the total cost of ownership guide and the payback period guide.
Trade-offs to weigh
Capital and lead time. An AS/RS is usually a large capital project, with design, manufacturing, installation, and commissioning before it ships an order. Budget for software, integration, and building work as well as equipment.
Fixed throughput. Output is capped by retrieval machines and ports. Adding capacity later can mean more aisles, robots, or ports, which may not fit the original design.
Less room to change. Rack heights, container sizes, and weight limits are set at design. A shift toward larger, heavier, or oddly shaped items can push SKUs out of the system.
Concentrated risk. When a crane, lift, or controller is down, the inventory behind it may be out of reach. Ask about redundancy, spare parts, and service response times.
Building and fire protection. Floor flatness and load capacity, clear height, and sprinkler design all need early engineering review with your fire protection engineer.
Re-storage. Inventory has to move into the system's totes, trays, or rack, which shapes your go-live plan.
None of these rules an AS/RS out. They explain why it suits stable, high-volume operations better than fast-changing ones. A widely cited literature review makes the same point from the design side: AS/RS requirements are increasingly dynamic, while most of the models it reviewed address static problems only.
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Questions to ask before you buy
What volume are you sizing for? Design to peak-hour demand, not an average day, and decide how many years of growth the system must absorb.
How much of your inventory fits? Find the share of SKUs and volume that fits the containers and weight limits, and where the rest will live.
What happens when a machine stops? Ask which inventory becomes unreachable, for how long, and what manual fallback exists.
How will it connect and change? Confirm who owns the WMS or WES integration and how new SKUs, rules, and order types are added after go-live.
What does service look like? Agree on spare parts kept on site, response times, and the in-house maintenance skills you will need.
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AS/RS vs other options
Goods-to-person AMRs. Robots bring shelves or totes to stations. Less dense than an AS/RS, but easier to expand in small steps or move to another building. See the AMR guide.
Existing shelving with robotic or assisted picking. Keep your current storage and add AMRs, pick-to-light, or mobile manipulators. Least disruption, least density gain.
Micro-fulfillment. Compact automated storage close to customers for fast delivery. See micro-fulfillment centers.
Better slotting in conventional racking. Sometimes the cheapest fix for space is warehouse slotting and better use of cube.
Where Avatar fits
If storage density is your main constraint, an AS/RS is likely the better answer. Avatar does not sell AS/RS or other storage systems. Its robots pick, pack, kit, sort, and cart in your existing racks and bins, so they suit sites that want to automate handling work without re-racking or redesigning the facility. Avatar runs on Robots-as-a-Service, with first production runs in weeks; see the Avatar solutions page.
How It Works
The process in four steps.
1
Induct and store
Inbound goods are checked, placed into the system's pallets, totes, or trays, and stored in locations the software assigns by size, weight, and demand.
2
Sequence the requests
Your WMS sends orders or replenishment tasks, and the AS/RS software sequences retrievals to keep machines and ports busy without collisions or idle waits.
3
Deliver to the port
A crane, shuttle, lift, carousel, or robot brings the load to a pick port or transfer point, where a person or robot arm takes what the order needs.
4
Return and update
The load goes back into storage, often to a new location chosen by demand, and the system updates inventory records as each move completes.
Frequently Asked Questions
What is an AS/RS in a warehouse?
An AS/RS is a computer-controlled system that stores loads in set locations and retrieves them automatically when an order or task needs them. It combines a storage structure, retrieval machines such as cranes, shuttles, or robots, pick or transfer stations, and control software linked to your WMS.
What are the main types of AS/RS?
The main types are unit-load systems for pallets, mini-load systems for lighter totes and cartons, shuttle systems, horizontal and vertical carousels, vertical lift modules, and cube-based robotic storage. They differ in load size, density, throughput, and how easily they expand.
How much does an AS/RS cost?
Costs vary widely by type, size, throughput, and building, from a single vertical lift module to a multi-aisle unit-load system. Budget for software, integration, installation, building work, and maintenance as well as equipment. Compare options on total cost of ownership and payback, not equipment price.
Is an AS/RS better than AMRs?
It depends on your constraint. An AS/RS wins on storage density and steady, high-volume throughput. AMR-based systems are usually easier to scale in steps, relocate, or change when your volumes and items shift.
Sources
1. MHI AS/RS Industry Group (n.d.). An Overview of Automated Storage and Retrieval Systems. MHI.
2. Roodbergen, K. J., and Vis, I. F. A. (2009). A survey of literature on automated storage and retrieval systems. European Journal of Operational Research, 194(2), 343–362.
3. Rogers, L. K. (2011). Equipment 101: Automated storage and retrieval systems (AS/RS). Modern Materials Handling, March 1, 2011.
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