File structures in Valve games
This information is from a Windows 10 computer. Some things may not apply for users on other operating systems. It may also be different if you have a non-standard installation of your operating system, Steam, or any game.
- C:
- Program Files (x86)
- Steam
- steamapps
- common
- Game Folders
- mod folders
- Game Folders
- sourcemods
- common
- steamapps
- Steam
- Program Files (x86)
C:
This is your system's C drive. It probably holds everything on your computer.
Program Files (x86)
This is where most 32-bit programs you download will be installed to if you have 64-bit operating systems. For 32-bit operating systems, only Program Files folder exist.
All 64-bit Steam games would install on this location.
Steam
This folder is where most data for Steam is kept on your computer.
steamapps
This folder holds all or nearly all games and mods. Most things outside of this folder are just for the Steam program itself. Such as ACF files which was used to show installed games on the Steam Library.
common
This holds all or nearly all the games (and some tools) you've downloaded from Steam. The folders in here are known as game folders. Some of them will have the exact same names as the game names on their Steam store pages.
game folder
The name of a game folder usually clearly states what's inside it; Portal 2 contains everything for the game, Portal 2. For Source games, this includes base engine things, such as Hammer and integration with Steam (for achievements, playing status, etc).
mod folder
Mod folders hold all the content that a regular player sees while playing a game. Mod folders can use content from other mod folders in the same game folder, using gameinfo.txt. Confusingly, one is also called a game directory sometimes.
Usually named after an abbreviation for a game, such as hl2 for Half-Life 2.
Folders under a mod folder will replace corresponding content inside a VPK. For example, if you put a file at modfolder\models\player\player.mdl, it would replace the file at VPKNAME.vpk\models\player\player.mdl.
List of all mod folders:
Alien Swarm: Alien Swarm\swarm
Counter-Strike: Global Offensive: Counter-Strike Global Offensive\csgo
Counter-Strike: Source: counter-strike source\cstrike
CS:S (Half-Life 2 content): counter-strike source\hl2
Counter-Strike: Half-Life\cstrike
Counter-Strike: Condition Zero: Half-Life\czero
CS Condition Zero Deleted Scenes: Half-Life\czeror
Day of Defeat: Half-Life\dod
Deathmatch Classic: Half-Life\dmc
Garry's Mod: GarrysMod\garrysmod
Half-Life: Half-Life\valve
HL: Blue Shift: Half-Life\bshift
HL: Opposing Force: Half-Life\gearbox
HLDM:Source: Half-Life 1 Source Deathmatch\hl1mp
HL:Source: Half-Life 2\hl1
Half-Life 2: Half-Life 2\hl2
HL2: Episode One: Half-Life 2\episodic
HL2: Episode Two: Half-Life 2\ep2
HL2: Lost Coast: Half-Life 2\lostcoast
HL2: Deathmatch: Half-Life 2 Deathmatch\hl2mp
HL2DM (HL2 content): Half-Life 2 Deathmatch\hl2
Left 4 Dead: left 4 dead\left4dead
L4D (The Sacrifice DLC): left 4 dead\left4dead_dlc3
Left 4 Dead 2: Left 4 Dead 2\left4dead2
L4D2 (The Passing DLC): Left 4 Dead\left4dead2_dlc1
L4D2 (L4D1 content): Left 4 Dead\left4dead2_dlc2
L4D2 (More L4D1 content and Cold Stream): Left 4 Dead\left4dead2_dlc3
Portal: Portal\portal
Portal (HL2 content): Portal\hl2
Portal 2: Portal 2\portal2
Portal 2 (Art Therapy content): Portal 2\portal2_dlc1
Portal 2 (puzzlemaker content): Portal 2\portal2_dlc2
Ricochet: Half-Life\ricochet
Team Fortress Classic: Team Fortress 2\tfc
Team Fortress 2: Team Fortress 2\tf
TF2 (HL2 content): Team Fortress 2\hl2
addons
This folder is not created by default in most games, but most plugins such as SourceMod and MetaMod: Source are usually installed on this directory.
In games such as Postal III, and all or most games since Left 4 Dead engine branch, this is where custom content was installed, such as: custom models, maps, sounds, etc...; In Left 4 Dead engine branch (or in some games), only VPK files were supported for custom content.
This folder was also used by Garry's Mod for it's custom content (such as Lua scripts, and other mentioned above). They either contains folders or GMA file.
cfg
Holds many configuration files. See CFG for more info on the files inside.
custom
(only in 
)
Similar to addons in Left 4 Dead engine branch games, except both folders and VPKs are supported.
logos
Contains spraypaints for a multiplayer game.
manual
Contains a manual explaining a multiplayer game.
maps
Holds all the BSP files for a game.
maps\workshop
For games that allow workshop content, maps downloaded from the workshop will be stored in here.
maps\graphs
Stores AIN files used by AI systems.
mapsrc
Usually not shipped with a game, but it's recommended you make and store VMFs in here so that your maps folder will not become cluttered.
media
Usually holds BIK files. (Video files for things such as the startup video)
models
Stores models.
particles
May hold manifest files (particles_manifest.txt) or PCF files.
puzzles
Contains automatic screenshots and P2C files of any Portal 2 tests you've made with the in-game puzzlemaker.
reslists/downloadlists
See Content_Streaming.
resource
Contains various files dealing with text and languages, and other VGUI resources.
SAVE
Contains all Save Game Files.
scenes
Contains scenes.image.
screenshots
Self-expanatory.
scripts
Contains many files defining properties for weapons, vehicles, soundscapes, and more.
.vpk
A VPK can hold most things one would find in the folders under a mod folder directory. Some things have to specifically be placed inside or outside of a VPK.
sourcemods
Usually, a Source mod that isn't available on Steam can be manually placed here. Steam will recognize a non-Steam mod if it is in this folder and the mod is configured properly.