In music production a librarian is software whose function is to organize and store program information for MIDI instruments and processors. Librarians can store thousands of different sets of patch data for each device in a given system. In other words, they store and organize the actual computer data the device uses to set itself up to make the various sounds it can make – the parameter data if you will. They sometimes employ databases so patches may be searched on key words or attributes of the sound. They can upload or download the data to and from instruments connected via MIDI by using strings of system exclusive commands. This makes it very easy to change the entire contents of program memory of a given device for each session or job needing to be done.