What is Emulation?

Understanding emulation from the ground up, explained simply.

The Simple Explanation

Imagine you have a book written in French, but you only speak English. You need a translator. The translator reads the French words and tells you what they mean in English. Now you can understand the book.

An emulator works the same way. Old video games were written in a "language" that only their original console understood. A Super Nintendo game speaks "Super Nintendo language." Your Steam Deck does not understand that language. The emulator is the translator that reads the game's instructions and converts them into something your Steam Deck can understand.

The result? The game runs on your Steam Deck as if you were playing on the original console.

How Emulation Actually Works

Every game console has hardware inside it: a CPU (the brain), a GPU (graphics processor), memory (RAM), and various other chips. When you put a game cartridge or disc in, the console reads the game data and its hardware executes the instructions.

An emulator recreates all of that hardware in software. Instead of physical chips, your computer runs code that behaves exactly like those chips would.

Step by Step

1. You load a game file
   This is the ROM or ISO file. It contains all the game data that was originally on the cartridge or disc.
2. The emulator reads the game's instructions
   Just like the original console would, the emulator starts reading the game's code byte by byte.
3. Each instruction gets translated
   The emulator converts each original CPU instruction into instructions your computer's CPU can understand and execute.
4. Graphics are rendered
   When the game wants to draw something, the emulator intercepts those graphics commands and draws them using your computer's GPU.
5. Audio is generated
   Sound chip commands are translated and played through your computer's speakers.
6. Input is captured
   When you press a button on your controller, the emulator converts that into what the original console would have seen.

This all happens thousands of times per second. For older consoles, modern computers are so fast that emulation is easy. For newer consoles, emulation requires more processing power because there is more to translate.

Why Some Consoles Are Harder to Emulate

Factor	Easier Emulation	Harder Emulation
Console Age	Older consoles (NES, SNES)	Newer consoles (PS3, Switch)
Hardware Complexity	Simple single-chip designs	Multiple custom processors
Documentation	Well-documented systems	Proprietary, undocumented hardware
CPU Architecture	Common architectures (x86, ARM)	Exotic custom architectures (Cell in PS3)

The PlayStation 3, for example, used a unique "Cell" processor that was completely different from normal computer CPUs. Emulating it required years of reverse engineering and optimization.

What is a ROM?

ROM stands for Read-Only Memory. In the old days, game cartridges contained ROM chips with the game data permanently burned into them. When people say "ROM" today, they mean a digital copy of that data saved as a file on your computer.

ROM vs ISO vs Other Formats

Term	What It Means	Used For
ROM	Copy of cartridge game data	NES, SNES, N64, GBA, etc.
ISO	Copy of CD/DVD/Blu-ray disc	PlayStation, Saturn, Dreamcast, Wii
CHD	Compressed disc image	Any disc-based system (smaller files)
CSO/ZSO	Compressed PSP disc image	PlayStation Portable
RVZ	Compressed Wii/GameCube image	GameCube, Wii
NSP/XCI	Switch game formats	Nintendo Switch

All of these are just different ways to store game data. Some are straight copies, others are compressed to save space. See the ROM File Formats page for detailed information on each.

Why Emulate?

There are many legitimate reasons to use emulation:

Preservation

Old game hardware eventually breaks. Cartridges degrade. Optical discs rot. Original consoles fail. Emulation preserves games so they can still be played after the original hardware is gone. Many classic games have never been re-released and would be lost forever without emulation.

Convenience

Instead of owning a dozen different consoles, you can play games from all of them on a single device. On the Steam Deck, you can carry decades of gaming history in your pocket.

Enhancements

Emulators often let you improve games beyond what the original hardware could do:

• Higher resolution graphics (4K, widescreen)
• Better texture filtering
• Save states (save anywhere, any time)
• Fast forward and rewind
• Cheats and mods
• Custom controller layouts
• Netplay (online multiplayer for games that did not have it)

Accessibility

Original games and consoles can be expensive, rare, or simply unavailable in some regions. Emulation makes gaming history accessible to everyone.

Development and Research

Game developers study old games to understand game design. Researchers use emulation to study gaming history. Homebrew developers create new games for old systems.

Is Emulation Legal?

This is the most common question, and the answer has nuance.

Emulators Themselves: Legal

Emulator software is legal. Courts have ruled on this. The emulator itself does not contain any copyrighted game code. It is original software that happens to interpret data in a way compatible with old hardware. This has been established in legal cases like Sony v. Connectix and Sony v. Bleem.

ROM Files: It Depends

This is where things get complicated. The games themselves are still copyrighted. Here is how it breaks down:

Scenario	Legality
Downloading ROMs for games you do not own	Illegal
Downloading ROMs for games you do own	Gray Area
Making your own backup from cartridge/disc you own	Legal (personal use)
Homebrew games (made for free distribution)	Legal
Abandonware (games no longer sold)	Still technically illegal

BIOS Files

BIOS files are also copyrighted by the original console manufacturer. The same rules apply. You can legally dump your own BIOS from hardware you own, but downloading them is technically illegal.

The Reality

Copyright holders rarely pursue individual users. They focus on distribution sites and large-scale piracy. That said, understand the legal landscape and make your own informed decisions.

Why the Steam Deck?

The Steam Deck is an exceptional emulation device for several reasons:

Hardware Power

The Steam Deck's AMD APU is powerful enough to emulate nearly every console up to and including the PlayStation 3 and Nintendo Switch. This is a massive range of gaming history in a handheld form factor.

Full Desktop Linux

Unlike locked-down mobile devices, the Steam Deck runs full desktop Linux. You can install any software, including emulators, without restrictions. No jailbreaking required.

Controls

The Steam Deck has a comprehensive control set: two analog sticks, a d-pad, ABXY buttons, shoulder buttons, triggers, trackpads, and gyroscope. This covers the input needs of almost any console ever made.

Portability

It is a handheld. You can play anywhere. This is perfect for emulation since many of the best emulated games are from handheld systems or work well in short sessions.

Steam Integration

Games can be added to your Steam library with artwork, appearing alongside your PC games. It looks and feels like a unified gaming experience.

Community Support

The Steam Deck emulation community is large and active. Tools like EmuDeck and RetroDeck make setup easy. Problems get solved quickly. Settings are shared and optimized.

Common Emulators

Here is a quick overview of the emulators you will encounter. More details are in the system-specific guides.

RetroArch

RetroArch is not an emulator itself. It is a frontend that runs "cores," each of which is an emulator. One program, many systems. RetroArch handles the user interface, save management, shaders, and more. The cores handle the actual emulation. This is the backbone of many emulation setups.

Standalone Emulators

Some systems are better served by dedicated standalone emulators that focus on one system:

Emulator	System	Notes
Dolphin	GameCube, Wii	Highly mature and accurate
PCSX2	PlayStation 2	Excellent compatibility, many enhancements
RPCS3	PlayStation 3	Demanding but impressive compatibility
PPSSPP	PlayStation Portable	Fast and polished
Cemu	Wii U	Great for Breath of the Wild era games
Ryujinx	Nintendo Switch	Rapidly improving, many playable games
Yuzu	Nintendo Switch	Development stopped in 2024
DuckStation	PlayStation 1	Modern, accurate, enhanced
melonDS	Nintendo DS	Accurate DS emulation
Citra	Nintendo 3DS	Development stopped in 2024
Flycast	Dreamcast	Fast and compatible
Xemu	Original Xbox	Still maturing, growing compatibility

A Brief History of Emulation