DOS Wasm X

🏆 World's first browser-based DOS emulator with native-speed, lag-free Roland MT-32 MIDI emulation — no plugins, no compromise.

This is a browser based DOS emulator designed around ease of use and stability. It is based on the newer DosBox-X codebase and thus supports both Windows 95 and Windows 98 installations. However if you just want to use DOS applications and games you can stay in DOS mode. To begin using it simply drag and drop any application or game files onto the emulator. You can then save your hard disk with the click of a button or just exit if you want to discard your changes. I went with a simple and clean interface to try and make it approachable and non-intimidating. The hard disk saves directly in your browser so you can come back later and continue where you left off. It's like your own personal virtual machine on the web!

Supports the following features -

• Fully web based application - using web assembly
• Roland MT-32 MIDI Audio Emulation (using Munt/mt32emu) with real-time LCD message display
• Save hard drive to the browser (512mb, 1 gig, or 2 gig options)
• Automatic support for a variety of file formats (Iso, Zip, Bin, Cue, Img, 7z)
• Customize RAM (32mb, 64mb, 128mb)
• Import/export files into and out of the emulator
• Export your entire hard disk image for local saving
• Load/change CD while emulator is running
• Floppy Disk Support
• Speed up/slow down emulator time
• Mobile mode
• On scren keyboard
• Gamepad support
• Customize Mouse Sensitivity
• Dark Mode
• Audio support
• Full screen
• Zoom controls
• Mouse capture
• Resize resolution
• Customize CPU speed
• Host the application yourself
• Customize startup hard drive image
• Send CTRL/ALT/DELETE
• Pause/Unpause
• Import existing IMG hard disk if you already have one

You can try it here: https://www.neilb.net/doswasmx/ (PS: No MT-32 supported!)

Try my repo here: https://anomixer.github.io/DosWasmX/ (PS: Full MT-32 supported!)

Hosting

You can host the app on your own web server. Copy everything in the dist\ folder to your web server. Alternatively, you can use the pre-configured GitHub Actions workflow to automatically deploy the dist/ folder to GitHub Pages when pushing to the master branch (ensure your Repository's Pages source is configured to "GitHub Actions" in Settings).

Also you can optionally configure a Default Hard Drive to load when users navigate to your application. After Saving/Configuring a Hard Drive locally you can export it from the advanced menu.

Then update the settings.js file with the path to your img file

var DOSWASMSETTINGS = {
    CLOUDSAVEURL: "",
    ISOURL: "",
    DEFAULTIMG: "https://www.yourwebsite.com/hdd.img"
}

Startup Script

You can automate a startup script by creating a "DOSWASMX.BAT" file. It needs to live in the root C:\ drive, not in any subfolder. At the root type "EDIT DOSWASMX.BAT" to create the file and put each command on a seperate line. Then save your file and the hard drive. Example -

Build Instructions

You will need a Linux environment to build DOS Wasm X

• create a folder outside of this repo to install emscripten
• git clone https://github.com/emscripten-core/emsdk.git
• cd emsdk
• ./emsdk install 3.1.49
• ./emsdk activate 3.1.49
• source ./emsdk_env.sh
• replace Binaryen with special version
  • replace the file wasm-opt in emsdk/upstream/bin/wasm-opt with the one from this repo code/wasm-opt
  • navigate to the emsdk/upstream/bin/ folder and run chmod +x wasm-opt
  • this is needed because default Binaryen does not support Exceptions and Asyncify together
  • huge credit goes to @Caiiiycuk for developing this!
  • see references below if you prefer to get wasm-opt directly from his releases page
• navigate back to the code folder in the DosWasmX repo
• run make
  • you will get a build error towards the end saying EM_CACHE_IS_LOCKED
  • to get past this error simply copy the faulting emcc command from the terminal and run it manually (See screenshot below)
  • this should succeed and then run make again to finish building
  • later builds should not get this error after you do this one time fix
• this process will update the main.js and main.wasm files in your dist folder
• now serve the dist folder from a webserver and Enjoy!

The emscripten installation above is a one time setup however you will need to always run source ./emsdk_env.sh from the emscripten folder every time you close the terminal and before running make. This is because the emscripten compiler does not get saved to the PATH

Docker

If you wish to run directly in a container, you can use the following command after installing Docker Desktop:

docker run -d -p 80:80 nbarkhina/doswasmx

Once it has started, you can open your browser to http://localhost.

Online Documentation

For more extensive guides and technical information please refer to our Online Documentation

Screenshots

Mobile Mode

Overlay

• There is also a built in Overlay menu which can be accessed by pressing the tilde key on the keyboard "~"
• This can be useful for getting at certain functions when using a Gamepad Controller or to access the onscreen keyboard

Installing Windows

DOS Wasm X supports installing Windows 95 or Windows 98 using your own copy of Windows. Simply drag and drop the ISO onto the startup page. DOS Wasm X will detect the Windows CD and begin the installation process. If you choose to Install Windows 95 you may get the error below. Simply click OK and then cancel when it asks you for the Path to the CD. This will allow you to continue with the installation. The reason for this error is because at this stage of the process the CD drivers have not yet been loaded. However after restarting Windows it will detect the CD Drive and finish installing the drivers successfuly. Always remember to shut down windows in the guest OS before exiting the page. This will automatically save your hard drive changes to the browser and prevent scandisk from running the next time you boot into Windows.

Roland MT-32 Support

DOS Wasm X supports Roland MT-32 emulation out of the box using Munt (mt32emu).

To enable MT-32 audio in games:

1. Make sure your games are configured to use Roland MT-32 or LAPC-I for music (usually configured via the game's SETUP.EXE or INSTALL.EXE).
2. The emulator will automatically attempt to fetch MT32_CONTROL.ROM and MT32_PCM.ROM from your web server's root. Make sure to place these two ROM files in your dist/ directory on your server. (Note: If you are deploying via the provided GitHub Actions workflow, these ROM files will be downloaded automatically during the deployment process, so you do not need to add them to your git repository.)
3. Local Development: When running locally with run.bat, the script will automatically detect if the ROM files are missing and download them from archive.org.
4. MT-32 LCD Display: When a game sends MT-32 LCD messages (e.g., song titles or patch names), they are displayed in real-time next to the page header as MT-32 LCD Messages: xxxxxxxxx.
5. Performance Recommendation: For the best audio quality and emulation speed, run the emulator in a dedicated, independent browser tab. Avoid running multiple active tabs with heavy tasks or playing audio simultaneously, to prevent resource competition that can cause audio stuttering.

Common DOS Commands

• DIR - Display list of files and directories
• CD - Change the current directory
• XCOPY - Copy Files
• DEL - Delete one or more files
• MKDIR - Create a directory

You can also type HELP at the command line to get a list of commands.

References

The Following codebases were used in some part in creating this app

• DOSBox-X (Core Engine)
  • https://github.com/joncampbell123/dosbox-x
• DOSBox Pure (Onscreen Keyboard)
  • https://github.com/schellingb/dosbox-pure
• JS Dos (JSDos Asyncify Module)
  • https://github.com/caiiiycuk/js-dos
• Binaryen with Exceptions and Asyncify
  • https://github.com/caiiiycuk/binaryen-fwasm-exceptions
• Emscripten
  • https://github.com/emscripten-core/emscripten

AI Agents Development Log

The integration and optimization of Roland MT-32 emulation were fully completed with the assistance of AI Agents. A detailed log of the development process — including compilation error fixes, performance optimizations, the MT-32 LCD display feature, and critical bug fixes such as the cwrap function signature mismatch — can be found in AGENTS.md.

Disclaimer

This app was made for fun and is not affiliated or associated with Microsoft.