The Flight Management Systems (FMS) consists of navigation radio receivers; inertial reference systems; air data systems; navigation, flight and instrument displays; flight control systems; engine and fuel system; and data link.These subsystems are managed and processed by the Flight Management Computer (FMC).
The FMC provides the primary navigation, flight planning, and optimized terminal routes and en route guidance for the aircraft and is typically comprised of interrelated functions such as navigation, flight planning, trajectory prediction, performance computations, and guidance.The FMC and associated databases are an essential part of modern airline avionics.An FMC typically contains three databases in addition to the basic operational flight program (OFP).

The first is a software options database which activates the optional functionality contained in the OFP that is desired by the operator.
The second is the model and engine performance database and contains all the aircraft performance data which allows the FMC to compute fuel burn, optimum altitudes and airspeeds, etc.
The third is the Navigation Database (NDB).

The NDB is contains all the information required for building a flight plan and processing that plan when airborne.
All these databases are stored in the FMC on an electrically erasable programmable read-only memory (EEPROM) card.Each of these databases can be updated via a data loader every 28 days.

AIRAC updated every 28 days contains read only data but the pilot is still able to enter fixes, phantom stations and adjust parameters according to how he needs it within certain limits

The NDB contains terminal and en route fixes; waypoints and navigation reference system (NRS) grid points; intersections; airways and radio navigation aids.It also contains airports; runways; STAR and SID; holding patterns; and instrument approaches such as VOR, non-directional beacon, area navigation (RNAV), required navigation performance (RNP), satellite based navigation system (SBAS), and ground based navigation system (GBAS).