What is the SCS file format?
The .scs file format is used for storing game data and mod archives for SCS Software's Prism3D engine titles - most commonly Euro Truck Simulator 2 and American Truck Simulator. The archive holds the game's virtual filesystem contents: 3D models, textures, unit definitions, sounds, and scripts, all packed into a single container the engine mounts at runtime.
.scs archives come in two on-disk forms. The native HashFS variant begins with the four-byte ASCII signature SCS#; entries are indexed by CityHash-style path hashes rather than plain filenames. The simpler variant is a standard ZIP archive renamed to .scs, recognizable by the PK magic bytes - these can be opened by renaming them back to .zip.
SCS files location
.scs mod files are stored in the game's mod folder. Game base data - base.scs, def.scs, europe.scs - ships as HashFS archives in the game's installation directory.
SCS files and companion assets
.scs archives are sometimes accompanied by separate .sii unit definition files, .tobj texture descriptors, and .pmg/.pmd model files when assets are distributed unpacked. Mod authors may lock a HashFS archive by stripping its filename table to discourage extraction.
Security & safety
RISK: MEDIUMThe archive itself is data, but .scs mods can include game scripts (.sii definitions, sound triggers) that the game executes, so install mods only from reputable sources (Steam Workshop, TruckyMods/the official forum) - random third-party 'mod' sites are a common vector for bundled adware or malicious download wrappers. A 'locked' HashFS mod that hides its filenames isn't malware by itself (authors lock to protect their work) but you can't audit its contents. Always back up your game profile before enabling unfamiliar mods, as bad mods can corrupt a save.
Format details
in a nutshell- SimCity Societies saved game (.scs) - Electronic Arts' SimCity Societies (2007) saves a city/progress as .scs - a save file, not a mod archive.
- Lotus ScreenCam screen recording script (.scs) - Obsolete 1990s Lotus ScreenCam screen-capture/playback script; the format is long dead.
Programs that open SCS files
Windows4 apps
7-Zip
Open-source Works only for the ZIP-based variant: rename a copy to .zip (or open archive directly) to browse contents. Fails on HashFS. 
SCS Extractor (official)
Free Drag the .scs onto scs_extractor.exe to unpack a HashFS archive into a folder. Closes instantly = it's HashFS v1-only build, ZIP-based, or a locked mod.
Euro Truck Simulator 2 / American Truck Simulator
Paid Don't 'open' the file - install it: copy the .scs into Documents\Euro Truck Simulator 2\mod, then enable it in the in-game Mod Manager.
Extractor (sk-zk, GitHub)
Open-source Modern command-line extractor that handles HashFS v1/v2 and ZIP-based .scs, including some recovery of stripped paths. 
macOS1 app
Euro Truck Simulator 2 / American Truck Simulator
Paid Place the .scs in the game's mod folder under Documents and enable it in the Mod Manager (macOS builds available). 
Linux2 apps
Euro Truck Simulator 2 / American Truck Simulator
Paid Place the .scs in ~/.local/share/Euro Truck Simulator 2/mod and enable it in the Mod Manager (native Linux builds exist).
Extractor (sk-zk, GitHub)
Open-source Run the cross-platform extractor to unpack HashFS/ZIP .scs archives. Technical details
deep spec| File signature | `SCS#` (hex `53 43 53 23`, HashFS variant) or `PK` (hex `50 4B 03 04`, ZIP variant) at byte offset 0 |
| Container format | HashFS (SCS Software proprietary) or standard ZIP archive - both use the `.scs` extension |
| Byte order | Little-endian |
| Compression | HashFS: zlib-compressed entries; ZIP variant: DEFLATE or STORED per entry |
| Encryption / locking | No built-in encryption; mod authors lock an archive by stripping the filename table, leaving entries addressable only by hash |
| Internal version byte | Byte immediately following `SCS#` indicates HashFS v1 or v2; v2 is current as of ETS2/ATS 1.50 (2024) |
| Path indexing method | HashFS: 64-bit CityHash-style path hashes; ZIP variant: standard central directory indexed by filename |
| Integrity checking | ZIP variant: CRC-32 per entry; HashFS: path hash verification at load time |
| Typical file size | A few KB (small mods) to several GB (full map/base-data archives such as `base.scs` or `europe.scs`) |
| Maximum entries | ZIP variant: 65,535 (ZIP64 removes this limit); HashFS: limited by hash table allocation |
| Supported platforms | Windows, Linux, macOS - wherever Euro Truck Simulator 2 / American Truck Simulator runs |
| Internal asset types | `.pmg`/`.pmd` 3D models, `.tobj` texture objects, `.sii` unit definitions, `.mat` materials, sounds, and scripts |
| MIME type | `application/octet-stream` (HashFS); `application/zip` (ZIP-based variant) |
| ZIP-based variant compatibility | Rename `.scs` to `.zip` to open in any standard archive tool such as 7-Zip; works only for the ZIP-form variant |
| Released | Prism3D archive used by SCS titles; current with Euro Truck Simulator 2 (2012) and American Truck Simulator (2016) |
| Latest version | HashFS v2 (1-byte-versioned 'SCS#' archive; used since ETS2/ATS 1.50, 2024) |
| Specification | modding.scssoft.com |
SCS conversions
Community Q&A
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