the book
This is what's in my ERAU Electronic Nav textbook, take it for what it's worth (I sure paid too much

)...Here it goes:
The FMS provides integrated operation and control of several managment systems to provide automatic lateral navigation (LNAV) and vertical navigation (VNAV) for optimum flight profiles and performance management.
It is compromised of the following components:
- Autopilot/Flight Director System (ADFS)
- Air Data Computer (ADC)
- Electronic Flight Instrument System (EFIS)
- Engine Indicators and Crew Alerting System (EICAS)
- Flight Management Computer (FMC)
- Inertial Reference System (IRS - IRU/INS)
- Radio Navaids
- Aircraft system sensors
- Mode Control Panel (MCP)
The FMC is the heart of the FMS. It contains 2 databases, one for navigation and the other for performance. The nav database includes:
-Airports, Airways, Instrument approaches, Company routes, ruways , published DP's and STAR's, waypoints, and navaids.
The performance database contains the data related to the aircraft aerodynamics considering the weight of the airplane and it's engines. Maintenance personnel can update it when changes are necessary.
Inputs to the FMC are made through the Control Display Unit (CDU). (I believe some call it the MCDU). ACARS can also be accessed through the CDU.
WHEW! Guess I didn't waste ALL my money down here at Riddle!

(just most) Sorry for any typos, it's early in the morning for me...3pm but oh well, it's Sunday. I skipped around the chapters to give you the basics...I'm not an expert, nor have any experience in FMS aircraft, so please don't blast me if anything's wrong. Ya'll experienced pilots know better than I do!! Basically the way I see it, the FMC takes all the information from the from various systems, nav and performance, includes information from the other systems such as the ADC, EICAS, etc. and computes pretty much everything you could possibly need to know for that flight. This ENTIRE system, the way i read it, is considered the FMS.
Correct me if im wrong! FLY SAFE!!!