1. A system for electronic storage of data objects, the system comprising at least a first, designated foreground data storage device and at least a second, designated background data storage device, the data storage devices being connectable by way of at least one releasable connection, and an interface engine adapted to manage the transfer of data objects to and from the devices and also between at least two of the devices when the at least two devices are connected to each other, and to generate a logical stack of all the data objects stored in the system, including an index list of identifiers relating to the data objects, the index list being visible from any one of the designated data storage devices whether connected to another designated data storage device or not.