Flight Simulator (FS2002 and FS2004) make no use of the registry during normal use other than indirectly (via a Windows system call) to pick up the application data path where FS9.CFG for the current user is stored. The FS2002/FS2004 installer uses the registry, but only to read/write the location of FS2004 on disk, but during normal use, FS2002/FS2004 will quite happily run without any registry entries at all.

For Flight Simulator add-ons, the situation very much depends on what type of add on it is, and whether the developer (or installer writer if different) has made use of the registry, either directly through choosing specifically to store settings there, or indirectly because the installer uses the registry as a matter of course.

All installers are different. The Visual Flight installers just provide the minimum registry entries to provide the standard entries in the Add/Remove Programs list, but other installers, particularly those based on InstallShield and similar, tend to make a lot of use of the registry, and can get fussy about uninstalling/re-installing if the registry entries are not as expected.

In addition to the above, installer writers or developers may elect to create and use entries in the registry for whatever reason. Pure scenery products cannot make any use of the registry during actual use, but anything which contains executable binary code such as gauges, modules or add-ons which run separately to the main FS execuatable can and often does use the registry.

Note: Default Flight Simulator installations (FS2002 and FS2004) have no dependency on the registry at all to the extent that the main FS2004 folder can simply be copied to another location to create a second installation.

One thing that is fairly common is for installers to read the FS2002/FS2004 path from the registry in order to correctly install or provide a sensible default location for FS2004 for the installer (though it is depressing how many don't bother and just assume that everyone has installed to the default C:\Program Files\Microsoft Games\... location).

In the situation where there is no registry entry, e.g. following a Windows re-install and restoration of Flight Simulator and related folders from a backup, it's well worth downloading and running either FS2002_is_here.exe or FS2004_is_here.exe from the Visual Flight FS2004 Toolkit. Simply drop the correct exe file into the main FS2002 or FS2004 folder and run it once - it will register the folder it's run from as the FS2002/FS2004 path in the registry.

Note: It is not known yet how FSX will use the registry.