Emulators

Emulators

20 emulators ship with GenX-DOS, driving 28 sub-systems between them. Some of the integrations were one-liners; others took a week of trial and failure. Each one has its own story page — the table below is the index.

The engines

Article	Sub-systems
Emulator-XRoar-CoCo	Tandy Color Computer
Emulator-atari800	Atari 400, Atari 800XL
Emulator-VICE-family	VIC-20, MAX, C64, C16, Plus/4, C128
Emulator-pet2001-Skibo	Commodore PET 2001
Emulator-gearcoleco-ColecoVision	ColecoVision
Emulator-jzIntv-Intellivision	Mattel Intellivision
Emulator-libretro-o2em-Odyssey2	Magnavox Odyssey²
Emulator-apple2js	Apple ][+
Emulator-tiny8bit-CPC	Amstrad CPC
Emulator-elkjs-Electron	Acorn Electron
Emulator-js99er-TI-99-4A	TI-99/4A
Emulator-jsvecx-Vectrex	GCE Vectrex
Emulator-apple1js	Apple I
Emulator-jsbeeb	BBC Micro, BBC Master 128
Emulator-EmulatorJS-NES-FCEUmm	NES
Emulator-Javatari	Atari 2600
Emulator-JS7800	Atari 7800
Emulator-WebMSX	MSX, MSX2
Emulator-JSSpeccy	ZX Spectrum
Emulator-JtyOne	ZX81

Eight of these share one copy of the EmulatorJS framework at emulators/_shared-ejs/ — the six VICE bundles, the Coleco bundle, and the NES bundle. All the EJS-specific gotchas live in Emulator-VICE-family; the Coleco and NES articles assume that context and only document what's different.

How a game launches

The same flow across every emulator:

1. The user picks a number in a GAMES menu.
2. N.bat runs the named launcher (e.g. sonic1).
3. sonic1.bat is a link: entry pointing at the emulator's URL.
4. The terminal opens that URL in a new tab via window.open(link, "_blank").

URL patterns vary per emulator. Each engine article documents its own.

DESKTOP vs PROMPT entries

Every emulator's GAMES menu has a "boot a clean machine" entry as item N+1. Labels match what the user actually sees on boot:

• PROMPT for > / Ok style command-line systems
• BASIC for systems whose BASIC banner is the boot screen (READY, Ready, READY.)
• DESKTOP for OS-driven machines (none currently — reserved for future 16-bit additions)

All seven VICE-family + 800XL bundles route through a small empty.prg for the BASIC entry; the PET (now under Skibo) uses the same empty.prg pattern via its own runtime; Spectrum, ZX81, and CPC pass no query at all (their emulators already drop to ROM BASIC with no software inserted).

Controls reference pages

Every emulator directory has a controls.html documenting its keyboard / joystick mapping. Same dark-amber DOS-flavoured style across all pages; the page-level CSS lives in emulators/_shared/genx-controls.css.

Per-game instruction pages at gamedocs/<platform>/<key>.html replace controls.html when a game has researched gameplay instructions. The genx-controls-link.js script reads ?game=, ?tape=, or ?rom= from the URL and routes to the matching gamedocs page, falling back to controls.html when no game param is present (prompt/BASIC entries).

Every emulator's main entry HTML carries a small bottom-right controls link (fixed position, semi-transparent, Wikipedia-style external-link SVG icon). The link sits in the entry HTML itself — play.html for the wrapped emulators, the upstream index.html for the URL-driven ones (jsbeeb, webmsx, jsvecx). It's not in the virtual filesystem; the DOS prompt's dir output shows only .bat launchers and menu scripts, never raw .html files.

Adding a new emulator

Same recipe each time:

1. Copy the deployed bundle into emulators/<name>/. Mirror with wget if it's hosted, or build from source if you must. Drop the upstream node_modules, the inner .git, any .gitignore that excludes deploy artefacts, and any upstream README.md / dev tooling.
2. Strip telemetry and external runtime fetches from the source's HTML and bundled JS/CSS before deploying. Each of these patterns has bitten us at least once:
   • Inline analytics (gtag(, umami, etc.) — jsbeeb and webmsx both shipped Google Analytics; removed both.
   • Framework-version checks like fetch("https://cdn.<framework>.org/.../version.json") — EmulatorJS does this on every bootstrap. Patched checkForUpdates() to a no-op return;.
   • Hardcoded NetPlay / multiplayer relay servers — Javatari had SERVER_ADDRESS: "webmsx.azurewebsites.net/" for keep-alive + WebSocket. Set the address to "" so any guarded address && … short-circuits and the wss:// URL becomes invalid.
   • CSS web-font @import rules pointing at fonts.googleapis.com — jsbeeb's Vite-built CSS had a Lato import. Strip it; fall through to the system-font fallback unless the visual difference matters.
3. Add the standard <noscript> overlay to every new HTML entry point — copy verbatim from any existing emulator page.
4. Write play.html if the emulator needs a key-based launcher. Skip if the emulator's own page already accepts URL params (BBC, WebMSX, JSVecX patterns). The wrapper reads ?game=<key>, fetches games.json, looks up {title, rom}, and boots the emulator with that ROM.
5. Bundle the ROMs under emulators/<name>/<roms-dir>/. archive.org and most preservation sites don't set CORS for direct browser fetch, so wrappers can't pull at runtime — every byte must be on the same origin.
6. Wire fs.js: each game's .bat gets a link: field pointing at the URL pattern above. Per-system GAMES menu follows the 45-char box format (see Customising the Filesystem) with 10 titles + a PROMPT/DESKTOP entry.

Multi-model platforms

Some platforms host multiple machines under the same vendor — ATARI has 2600 / 7800 as siblings under CONSOLE and 400 / 800XL as siblings under HOMECOMP; MSX has MSX1 and MSX2; SINCLAIR has SPECTRUM and ZX81. The hierarchical pattern: a parent menu with 1.<MODEL1> / 2.<MODEL2> rows, each pointing into its own GAMES dir. See prompt/javascript/fs.js for the exact tree.

Single-platform manufacturers (NES, INTV, CVISION, ODYSSEY2, VECTREX, COCO) sit directly under their CONSOLE or HOMECOMP parent — no manufacturer middle level.

Note: Atari 400 + 800XL share one emulator build (emulators/atari800/). The menus differ only in which ?machine= URL param their launchers pass.

Testing changes

./serve.sh        # or: python3 -m http.server 8765

After editing fs.js or any emulator wrapper, hard-refresh the prompt page (Ctrl+Shift+R). Browsers aggressively cache fs.js between visits.

Related

• Project Overview — what the site does
• Virtual Filesystem — how .bat launchers reach play.html
• File Structure — where bundles sit in the repo
• Roadmap — what's shipped, what's next