If a 'master' file is missing when the game starts, this CTD can occur during or even before the 'loading screens' are displayed. Usually this results in a 'Crash To Desktop' (CTD). The game engine requires that a 'master' be loaded before a 'dependency' or it generates an error. but still should be above any dependent plugins. In addition, an ESP file from one mod may be required by another ESP, in which case it is also considered a 'master' even though in all other respects it is 'just an ESP' and may appear lower in the 'load order'. Thus an ESP file can have the flag enabled and be treated as if an ESM file to include loading with other ESM files at the top of your 'load order'. A file is technically considered an 'ESM' because it has that flag enabled in the file header, which is normally not visible to the player. Typically these 'masters' have an ESM file extension, but this is just a general guideline. The files which require some 'master file' are known as 'dependencies', because they 'depend' upon the assets of the 'master'. Remember that the capabilities of 'Construction Set' tools vary by game but the concepts related to the same game engine endure.)Ī 'master file' is one which must be present for another plugin to be able to utilize it's resources. (For the technical distinctions between an ESM and an ESP, see this ESP vs ESM wiki article. 'FalloutNV.ESM') so it should always be first. All DLC depend upon the game's original ESM file (i.e. DLC are usually sequenced in the order they were released but this is not mandatory unless they depend upon an earlier DLC. Official game expansions ('downloadable content', known as 'DLC') typically are provided as ESM files along with other 'assets'. The ESM files are loaded first, and are considered 'masters' to the ESP files that depend upon them. There is generally only one ESM file, but there may be any number of ESP files (including none).

'Plugin' files have one of two possible file extensions: ESM and ESP. The 'plugin' files are the only ones that appear in the 'load order', which determines the sequence in which the game engine loads them into the game from the 'top' (lowest numbered) to the 'bottom' (highest numbered) position in the sequence. Within a 'mod' package can be a number of 'asset files' which add to or replace the existing vanilla assets (meshes, textures, sounds, animations, XML files, etc.), and one or more 'plugin files' that tell the game about the existence and use of the new assets and where they are placed in the game.

A 'mod' is a package (archive) of related files that make some change to the 'vanilla' (unmodded as delivered by the publisher) game.

Fallout 4 vanilla extensions