The Directory Structure of Microsoft's
Flight Simulator X tm

By default, Flight Simulator is installed in C:\Program files\Microsoft Games\Flight Simulator X.  I suggest installing it instead in C:\Flight Simulator X, or any other disk you want to put it on.  The shortened pathname could result in better performance for you, especially if you install photoreal sceneries.  In fact, it is a good idea to put your FS installation on a separate disk than that used for your operating system and virtual memory/swap space.

Within Flight Simulator X, there are 8 important directories you should know:

\Flight Simulator X
    \Addon Scenery
    \SimObjects (Originally the "Aircraft" directory)
    \Effects
    \Gauges
    \Scenery
    \Sound
    \Texture
    \Autogen
    \Missions

Addon Scenery:
This directory typically contains scenery you add to FS.  By default, it contains two directories - Scenery and Texture.  Each FS9 scenery library has this directory structure.  The Scenery directory contains the scenery files (.bgl files) that describe the objects (buildings and airport objects (runways, etc.), mesh, landclass) in the scenery and where they should be put.  The Texture directory contains the files (.bmp, .dds, .r8, .agn files) which tell FS what the surfaces of these objects look like.

As noted FS Scenery is made up of several different objects.  At the first layer is the mesh.  Mesh describes what the terrain looks like, in other words, the hills, mountains, plains, and gullies the rivers lie in.  Laid over the terrain are textures.  A texture is basically a picture which is laid onto a surface.  These textures are laid out according to rules called "landclass".  A landclass texture will look like a top down view of a field, or a forest, or a city block.  The landclass rules tell FS where to put these textures to make the ground look like forest, fields, cities, etc..  Then on top of this, FS draws the 3D objects (i.e. Buildings, cars, etc.), runways and roads and rivers/lakes.  Every surface of every object has an associated texture file.  Some texture files contain the information to cover many different surfaces.

You could just throw all the scenery files you download into these two directories, Scenery and Texture.  It is a better idea, however, to create a separate library for each scenery you download.  For instance, to install Nashua airport, you would create a directory Addon Scenery\KASH, which in turn would contain two directories, Scenery and Texture, like:

\Addon Scenery
    \KASH
        \Scenery
        \Texture

You can also create scenery libraries with the same structure in other locations.  In fact, this is recommended for large area photoreal sceneries, which can contain thousands of files.  Photoreal libraries should be installed at the root directory of the drive you install them, e.g.:

D:\Megascenery New York
    \Scenery
    \Texture

In most cases, however, it is good enough to install the scenery library in Flight Simulator 9\Addon Scenery.

Once you have copied the scenery files to the new library directories, you will need to:

1. Start FS and select Setting\Scenery Libraries.
2. Select "Add area".
3. Select the directory you just created, e.g. Addon Scenery\KASH.  Do NOT select Addon Scenery\KASH\Scenery.
4. Select Ok to finish adding the area.
5. Finish whatever other library management tasks you want to do (i.e. move libraries up and down to change their priority, add other areas, etc.).
6. Select Ok and continue using FS.  You no longer have to quit Flight Simulator after you make changes to the Scenery Library..

SimObjects:
This directory contains several directories for the various dynamic objects in FSX.  This is a big change from FS9.  The main objects you will be concerned with are your aircraft, found in the "SimObjects\Airplanes" directory by default.  The structure of each of the objects is basically the same.  And you no longer have to add your aircraft to the default aircraft directory anymore, as you can now declare the path to the various components of a SimObject.  Unlike scenery libraries, FS automatically reads aircraft you install from here.  Unfortunately, that means this is the only place you can install aircraft, which can make their management unwieldy.  Each aircraft contains a standard set of directories and files, the minimum being:

Airplanes
    \XXX
        \Model
            XXX.mdl <-- binary file describing what model looks like
            model.cfg <-- text file describing which .mdl file to use
        \Panel
            background.bmp <-- Picture describing what the 2D panel looks like
            panel.cfg <-- text file describing which gauges to use, where to put them,
                                            and what the background looks like for each panel
        \Sound
            yyy.wav <-- a sound file for each sound the airplane makes
            sound.cfg <-- a text file describing when to play each sound file
        \Texture
            zzz.bmp <-- a picture file(s) containing a picture for each surface in the model
        aircraft.cfg <-- a text file describing various aspects of the airplane,
                                        including engine type, description, associated effects, flight characteristics, etc.
        XXX.air <-- a binary file containing many of the flight characteristics of the airplane

There are other files as well, such as checklists and reference files, that are easy enough to discover what they are by looking at their contents.

Effects:
This directory contains files describing the effects in FS, such as how bright or what color lights should be, afterburner effects on jet engines, smoke, etc.  This directory normally contains all the effects files used in FS.

Gauges:
This directory contains the instrument panel gauge files.  When you install a plane, you will typically copy the gauges for the panel here.  If the gauges are stored in .cab archive files, the gauges can also be in the aircraft\XXX\panel directory instead.  It is harder to share gauges between planes, however, if they are installed only to the panel directory.  So usually, most gauge files are stored here, since many gauges are often shared among airplanes.

Modules:
This directory contains special code libraries for flight simulator to use.  Normally, you will not have to deal with this directory very often.  The very important fsuipc.dll file goes in this directory.

Scenery:
This directory contains the default scenery files.  It contains several scenery libraries:

\Scenery
    \0000 - 1107 <-- Default scenery (Airports, Roads, Scenery
    The next Directories contain the "special" scenery for detailed cities in each region     \Afri <-- Africa
    \asia <-- Asia
    \Aust <-- Australia and Hawaii
    \Base <-- Base scenery - Landclass, timing of seasons, global low level mesh
    \Cities <-- Photoreal libraries for a number of cities
    \Default Mesh <--Not a default library - see "Installation" for instructions on why I create this library.
    \Eure <-- Europe, Eastern
    \Eurw <-- Europe, Western
    \FSGLC <-- Not a default library - This is where I install FSGenesis Landclass file (inside FSGLC\Scenery)
    \Global <-- Generic object libraries; trees, bridges, landmarks, vehicles, etc.
    \Namc <-- North America, Central
    \Name <-- North America, East
    \Namw <-- North America, West
    \Ocen <-- Oz
    \Props <-- ?
    \Same <-- South America
    \World <-- Normally contains the textures for the landclass, the detailed mesh .bgl files, and AI Traffic description files
    \... <-- any other directories for products you might install here, like the "Ultimate Terrain" products, or other mesh libraries (or can go in Addon Scenery, too)

Sound:
Contains globally used sound files for various sounds in FS.  Not many products install files here.

Texture:
For globally shared object texture files.  If FS cannot find a texture file in a library's local texture directory, it will look here for the file.  This is a good place to put textures that are shared between multiple libraries, so the file need only be installed once.