An automated storage and retrieval system wherein electrically driven, computer-controlled carriages (58) can navigate a system of rails (78) in three-dimensions. Multiple carriages (58) can independently operate at the same time to accomplish a task faster or to work on several different tasks at the same time. The rails (78) have a system of trap doors (95) that allow a carriage (58) to use a single reversible motor (67) to navigate the rails (78) in three-dimensions. With the carriage (58) in positioned in font of a bin position, the carriage mounted manipulating device (125) can move bins (115) to and from the racks (107) from either side with a single reversible motor (131). The rails (78) are electrified to provide power for the drive (67) and manipulator motors (131). A main computer (146) maintains the inventory, handles transactions and assigns tasks to the computer-controlled carriages (58). The system can be scaled to handle different types of items and can be configured to fit in the space available.