Storage and retrieval system

A storage and retrieval system, comprising:

• a frame having at least two columns adjacent to one another;
• a track disposed within each column, each track being generally parallel to one another;
• a plurality of storage units that reside and move within the tracks of each column;
• an actuator coupled to the frame for displacing one or more storage units in one or more of the columns;
• a first upper conveyor comprising a vertically hanging hook selectively movable for drop-hang engagement with a catch top-mounted to each storage unit for movement of at least one storage unit between a first position in one column and a first position in another column;
• and
• a second lower conveyor comprising a skid selectively movable between the at least two columns for supporting the bottom of at least one storage unit and carrying said storage unit in non-sliding relation between a second position in one column and a second position in another column;
• wherein sequential activation of the actuator, the first conveyor, and the second conveyor permits sequential clockwise or counterclockwise movement of the plurality of storage units within the frame.