A RIDS system is composed by a database server, a network of clients (displays or operator workstations) and by a certain number of Application Servers; this number depends on the number of clients and may be increased at any time in case of expansion of the display network.
A three-tier architecture - a.k.a. three-layer architecture (emerged to overcome the limitations of the two-tier one) - includes a middle tier server between the user interface (client) and the database server components. The three tier architecture is used when a RIDS design needs increased performance, flexibility, maintainability, reusability, and scalability.
This software architecture is easily scalable from very small systems (with tens of displays) to very large systems (thousands of displays possibly distributed in several terminals).
A RIDS is usually considered a mission-critical system, beacuse is has to provide passengers with accurate and up-to-date information on their trains, in order to lead them on the right path through the station, up to the appropriate platform. Train data is also vital for most personnel and for management, so it is mandatory that data are never lost and to ensure a continuous service, with minimal disruptions or none at all.