Project Overview

Project Overview

GenX-DOS is a static page that recreates a 1990s DOS prompt in the browser. Visitors land on a fake AMIBIOS POST screen, get dropped into a C:\> prompt, and navigate numbered menus to launch emulated games — all running locally in the page.

There's no server, no build step, no framework. The whole thing is HTML and JavaScript that runs straight out of GitHub Pages.

The boot flow

When the page loads:

1. index.html does an instant <meta refresh> to prompt/. The actual POST animation lives inside the prompt page.
2. prompt/index.html is the DOS terminal. On load, init():
   • renders the AMIBIOS POST — AMI logo, AMIBIOS header, CPU/coprocessor/memory test with animated 0000 → 8064 KB count, six device-detection lines streamed at 500 ms each, footer with BIOS ID
   • pauses 5 seconds with the full POST on screen — and yes, the Hit <DEL> if you want to run SETUP prompt is live. Press Delete during the pause and you get the CMOS password box (white on BIOS blue). There is no password. Esc backs out to the POST (pause re-armed, Delete still live), but three wrong attempts turn the box red with System Halted! — keyboard dead, reload to reboot. AMI would be proud.
   • clears, renders the System Configuration table
   • prints Starting GenX-DOS . . . and Type "help" <enter> for assistance.
   • calls initTerminal() which wires up the keyboard and runs AUTOEXEC.BAT
3. AUTOEXEC.BAT runs menu. The root menu.bat does cd systems\menu, dropping the user straight into the EMULATOR LAUNCHER.
4. The user types a number (or a command name) to navigate.
5. Selecting a game opens the emulator in a new tab via window.open.

How it's built

Pure HTML + JavaScript. No build step, no frameworks, no dependencies.

Every visible character is its own <div>, styled with a CSS background-position into a 12×12 CP437 sprite sheet. The virtual filesystem is a JS object tree in prompt/javascript/fs.js. When the user types dir, the prompt walks that tree and renders the result through the sprite font.

Save / load state

Most bundles carry save / load controls (bottom-left); each opens a drop-up menu of five save slots per game — an instant in-browser snapshot of the running machine, held in memory and persisted to IndexedDB (keyed platform:game:slot) so the slots survive a reload, and different games are kept independent. The 14 EmulatorJS bundles drive the libretro cores' state API via _shared/genx-savestate.js; the standalone engines that expose a reachable save-state — TI-99/4A, BBC Micro/Master (mid-game, even Elite), MSX, CoCo, Odyssey², Atari 8-bit and Amstrad CPC — register a per-bundle GenXStateAdapter that _shared/genx-savestate-std.js wires to the same menus. Each engine reaches it differently (processor.snapshotState(), WMSX.room.machine.saveState(), XRoar's write_snapshot, the o2em retro_serialize rebuild, atari800's deferred StateSav_*, the cpc cpc_save_snapshot rebuild…), documented per page. Three (Odyssey², Atari 8-bit, Amstrad CPC) needed a WASM rebuild to expose state the stock build hid. The engines with no reachable state API (Apple, Electron, Spectrum, ZX81, Intellivision, PET) — plus the TRS-80, whose sdltrs has a built-in but unwired save-state — have no buttons.

The scope rule: 8-bit feel

Every shipped system has the feel of an 8-bit machine — sprite-based, chiptune, low-res. The test is the aesthetic, not the calendar year or strict CPU bit-width. (Updated 14/06/2026 from the earlier "8-bit era, ~1975-1990" framing.) Intellivision (CP1610, 16-bit ALU) is in because it plays like an 8-bit-era console. The 8-bit-feel handhelds — Game Boy / GBC, Game Gear, Lynx — are in even where they run into the late 90s (a colour GBC game from 2002 still feels 8-bit). Sega Genesis (1988) is out: it defined the 16-bit look-and-sound leap, even though the calendar year overlaps.

DOS is the prompt host. See Roadmap for the full in/out list and what's still on the slate.

The lineup

18 emulators ship under systems/, driving 32 sub-systems:

• Consoles: Atari 2600, Atari 7800, ColecoVision, Intellivision, NES, Magnavox Odyssey², Sega Master System
• Handheld: Game Boy / Game Boy Color, Atari Lynx, Sega Game Gear
• Apple: Apple I, Apple ][+
• Acorn: BBC Micro, BBC Master 128 (same jsbeeb engine, shipped as two bundles — bbcmicro/ boots Model B, bbcmaster/ boots ?model=Master), Electron
• Atari home: Atari 400, Atari 800XL (same atari800 engine, shipped as two bundles — atari400/ boots OS-B, atari800/ boots OS-XL)
• Commodore: VIC-20, MAX, C64, C16, Plus/4, C128 (six sub-systems off four VICE libretro cores); PET on its own (Thomas Skibo's pet2001, vanilla JS)
• Sinclair: ZX81, ZX Spectrum
• Amstrad: CPC
• Tandy: CoCo, TRS-80 Model I
• Texas Instruments: TI-99/4A
• MSX: MSX1, MSX2

Fourteen of these (the six VICE bundles, ColecoVision, NES, the Atari 2600, the Atari 7800, the Sega Master System, and the three handhelds — Game Boy/GBC, Lynx, Game Gear) share one copy of the EmulatorJS framework via systems/_shared-ejs/. Intellivision, Electron, Odyssey², and the PET stand alone — jzIntv, ElkJS, libretro-o2em, and Skibo's pet2001 respectively, each with its own custom loader.

See Emulators for the index and individual integration stories.