The original game file is fetched and handed to an emulator that has been compiled to WebAssembly and runs inside the browser tab. The emulator reproduces the console's processor, video chip and sound hardware in software, then executes the game's own unmodified code against them.

Nothing is installed on your computer and nothing runs after you close the tab.

No. Everything needed — emulator and game — arrives as part of the page. There is no launcher, no browser extension, and no account.

A save state is a snapshot of the whole emulated machine at one instant: every byte of memory, the state of the video chip, the position of the processor mid-instruction. Reloading it puts you back exactly where you were, mid-jump if that is where you stopped.

The game's own save — a battery-backed file or a password — only records what its developers chose to store, and only at the points the game allows. That is why a save state can rescue you three pixels before a pit and an in-game save cannot.

Save states are written to your browser's IndexedDB storage, which belongs to that browser on that device. They survive closing the tab and restarting the machine.

They do not follow you to another browser or another computer, and clearing site data deletes them. The Export button writes a state to a file you keep, which is the only copy that is really yours.

Yes. Any USB or Bluetooth controller the browser recognises through the Gamepad API works — connect it, press a button so the browser registers it, and it is picked up. The keyboard layout for each system is listed beside the player if you would rather not.

Because each version was rebuilt for different hardware rather than copied. The Mega Drive/Genesis produced sound with an FM synthesis chip, while the SNES played back short recorded samples — which is why one sounds bright and metallic and the other warmer, playing the same tune.

The same applies to what you see: colour counts, sprite limits and screen resolution all differed, so artists redrew the game for each machine.

Many began as arcade machines, where difficulty was the business model — a game that lasted too long on one coin did not earn. Home conversions usually kept that balance.

Cartridge space pushed the same way. When you cannot fit forty hours of content into the memory available, you make the few hours you have demand repetition and mastery instead.

For the design conventions most later games are built on, the NES. For the polish those ideas reached before 3D arrived, the SNES or the Genesis. For seeing how much can be done with almost nothing, the Atari 2600, which had 128 bytes of memory and no frame buffer.

DOS is a different tradition altogether — adventure games, simulations and strategy that never had a console equivalent.

Game sizes span three orders of magnitude here, from around 2 kB for an early Atari cartridge to several megabytes for a late DOS release. Each one downloads once and is then cached by your browser, so a second visit starts immediately.

Where the game itself has a two-player mode, yes: player one takes the arrow keys and player two uses WASD. Two connected gamepads work as well, which is usually the better arrangement for anything that needs fast input.

Modern mobile browsers run the emulators, and on-screen controls appear over the game. How well it plays depends on the device and the system — 8-bit consoles are undemanding, while later hardware such as the Nintendo 64 asks considerably more of a phone.

A core is one particular implementation of a system's hardware. Several usually exist for the same console because they make different trade-offs: a more accurate core reproduces awkward hardware behaviour that some games depend on, at the cost of running heavier.

If a game stutters, drops sound, or misbehaves on the default, the emulator list further down a game page lets you pick another. It is the first thing to try.

Audio breaking up is almost always the emulator failing to keep a steady frame rate. Close heavy tabs, try fullscreen, and switch to a lighter core.

Browsers differ more than people expect — Chromium-based ones currently compile WebAssembly faster than the alternatives, which shows most on the demanding systems.

Emulator software itself is lawful; it is an independent reimplementation of hardware, not a copy of anyone's game. The games are a separate matter, and it varies title by title and country by country: some were released by their authors as freeware or into the public domain, while many remain owned by companies that still trade on them.

We take removal requests seriously and act on valid ones — the DMCA page has the form. This is a description of how we operate, not legal advice.

Catalogue metadata — release year, publisher, genre — is imported from public retro-gaming databases, and the attribution and licence terms for that material are set out at the bottom of every game page.