What is the OS file format?
A .os file is a plain-text source code file written in ObjectScript, a lightweight JVM-based scripting language developed as an open-source project on SourceForge in the late 1990s and early 2000s. The language was designed to bring object-oriented programming concepts to a scripting environment, with code compiled or interpreted on the Java Virtual Machine.
ObjectScript source files contain class and object definitions, method implementations, and executable statements. The syntax shares structural similarities with Java source files - class-based layout, typed constructs, and method blocks. Because the format is plain text with no magic bytes or embedded signature, a .os file is identified solely by its extension; any text editor can open and read the code directly.
Important disambiguation: the .os extension is heavily overloaded by unrelated formats. Most notably, the InterSystems Caché and IRIS database platform has its own language also called ObjectScript, but that system stores code in .cls, .mac, and .int files - not .os. The extension also appears as compiled object segments or OS image files in other toolchains.
The SourceForge ObjectScript project is now dormant, having been effectively superseded by mainstream JVM scripting languages such as Groovy and general-purpose languages like JavaScript. Files are a cross-platform artifact - any system with a compatible Java runtime and the ObjectScript engine could run them.
Source files are typically small (under 200 KB per module) and can be edited in Visual Studio Code, vim, gedit, or any plain-text editor.
Security & safety
RISK: MEDIUMA .os ObjectScript file is source code, not a compiled binary, so reading it in an editor is safe and is the best way to see exactly what it does. But it IS a script: if you run it through the ObjectScript interpreter it executes whatever it contains, so review unfamiliar code before running. Also be careful identifying the file - if your '.os' is actually an OS image or a binary data/settings file rather than source, it should be handled as that format, not opened in a code editor.
Format details
in a nutshell- Operating-system / disk image file - Some tools and emulators use .os for an OS image or system file; binary, unrelated to source code.
- OmniScan data file (Olympus NDT) - Ultrasonic/NDT inspection data from Olympus OmniScan instruments uses .os in some workflows.
- Generic 'OS' settings/state file - Various applications drop .os files for operating-system-specific settings or saved state.
Programs that open OS files
Windows3 apps
Visual Studio Code
Free Open the .os as text to read/edit the source. No dedicated ObjectScript extension is needed for plain viewing. 
ObjectDevel / ObjectScript interpreter
Open-source The original (dormant) ObjectScript development tool - needed only to RUN the script; requires a Java environment. Treat as legacy. 
macOS1 app
Visual Studio Code / any text editor
Free Open as text to read the source. Running requires the ObjectScript runtime + Java. 
Linux1 app
Any text editor (VS Code, gedit, vim)
Free Open as text. The legacy ObjectDevel/ObjectScript engine runs on the JVM if you need to execute it. Technical details
deep spec| File type | Plain-text source code |
| Language paradigm | Object-oriented scripting language |
| Execution model | Compiled or interpreted on the Java Virtual Machine (JVM) |
| Character encoding | ASCII or UTF-8 |
| File signature | None - identified by .os extension only; no magic bytes |
| MIME type | text/plain (informal: text/x-objectscript) |
| Typical file size | 1 KB - 200 KB (a single source module) |
| Runtime requirement | Java Virtual Machine plus the ObjectScript interpreter/engine |
| File structure | Class and object definitions, method declarations, executable statements |
| Extension ambiguity | Heavily overloaded: .os also appears as compiled object segment files and OS image files in unrelated toolchains |
| Project status | Dormant - the SourceForge ObjectScript project is inactive; files are legacy artifacts |
| Compiled output | Produces JVM bytecode (.class files) when compiled |
| Developer / origin | Open-source ObjectScript project hosted on SourceForge |
| Platform support | Cross-platform: Windows, Linux, macOS - any system with a compatible JVM |
| Disambiguation | Unrelated to InterSystems ObjectScript (Caché/IRIS), which uses .cls, .mac and .int extensions |
| Superseded by | Groovy, JavaScript (Rhino/Nashorn), and Python for JVM-based scripting tasks |
| Released | Late 1990s - early 2000s (ObjectScript language, SourceForge project) |
| Latest version | ObjectScript project is dormant; no active versioned release of the .os format |
| Open standard | Yes · royalty-free |
| Specification | objectscript.sourceforge.net |
OS conversions
Community Q&A
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