The mechanisms necessary to install an applet on smart cards using Java Card technology are embodied in an on-card component called the Installer.

To the CAD the Installer appears to be an applet. It has an AID, and it becomes the currently selected applet when this AID is successfully processed by a SELECT FILE command. Once selected on a logical channel, the Installer behaves in much the same way as any other applet, as follows:

• It receives all APDUs dispatched to this logical channel just like any other active applet.

• Its design specification prescribes the various kinds and formats of APDUs that it expects to receive along with the semantics of those commands under various preconditions.

• It processes and responds to all APDUs that it receives. Response to incorrect APDUs include an error condition of some kind.

• When another applet is selected on this logical channel (or when the card is reset or when power is removed from the card), the Installer becomes deselected and remains suspended until the next time that it is selected.