Data cartridge caddy presence sensing method and apparatus

A data cartridge caddy presence sensing system within an autochanger storage rack is disclosed. The data cartridge caddy of the present invention has at least one optical interrupt flag at a predetermined position on the data cartridge caddy. When the data cartridge caddy is fully installed within the autochanger storage rack, the optical interrupt flag lines-up with and trips optical interrupt flags on the autochanger storage rack. The picker of the autochanger will not attempt to remove data cartridges from caddy positions that are empty. The present invention may also include optical interrupt flags and sensors on the data cartridges and corresponding optical interrupt sensors at corresponding predetermined locations on the autochanger storage rack or a bar-code reader and bar-code labels on the data cartridges. In such an embodiment, the autochanger picker will not attempt to remove data cartridges that are known to not be present within the data cartridge caddy and will not attempt to install a data cartridge in a slot in the data cartridge caddy that already has a data cartridge in it.