What is the ROM file format?
.rom files are game image files used by emulators to run console and computer games. A .rom file is a byte-for-byte dump of a game cartridge or ROM chip - the term "ROM" stands for Read-Only Memory, referring to the original read-only hardware the data was copied from.
Unlike dedicated formats such as .n64 or .smc, the .rom extension is a generic label with no fixed internal structure or magic bytes. Its internal layout depends entirely on which console or computer the dump came from - an N64 game, an MSX computer title, a ColecoVision cartridge, and a Game Boy game all produce very different binary layouts even though each might be saved as .rom.
Games for Nintendo 64 use several closely related formats alongside .rom:
.n64- little-endian byte order.v64- byte-swapped (interleaved) byte order.z64- big-endian byte order (the native N64 format)
To open a .rom file you need an emulator for the correct system. For N64 games, popular choices are Project64 and Mupen64Plus. RetroArch and OpenEmu support .rom files from many different systems through their core plug-in systems.
Because .rom carries no embedded system identifier, some emulators may be unable to auto-detect which console the file belongs to and may require manual configuration.
Security & safety
RISK: MEDIUMA game ROM is passive data the emulator interprets, so the file rarely runs on your real OS - but real risks exist. ROM download sites are a notorious source of malware and fake 'roms.exe' droppers, so only use reputable sources and scan downloads. Crucially, a .rom that is actually firmware/BIOS is dangerous in a different way: flashing the wrong firmware image to a motherboard, GPU or router can permanently brick the device - verify it matches your exact hardware before flashing. Legally, downloading copyrighted ROMs you don't own is generally infringement; dumping your own cartridges and homebrew/public-domain ROMs are the safer paths.
Format details
in a nutshell- Firmware / BIOS image - Motherboard BIOS/UEFI, GPU video BIOS (vBIOS), router and device firmware are often distributed as .rom files flashed onto the chip - not games.
- Option ROM / expansion ROM - PC add-in cards (network, RAID, GPU) carry an option ROM image, sometimes named .rom, loaded by the system firmware at boot.
Programs that open ROM files
Windows3 apps
Project64
Open-source Nintendo 64 emulator - File > Open ROM and pick the .rom/.z64/.n64/.v64 to play it. 
RetroArch
Open-source Multi-system emulator front-end. Load the ROM with the core for its console (e.g. Mupen64Plus for N64). Handles dozens of systems in one app.
Emulator for the right system (SNES9x, Snes/Nestopia, mGBA, etc.)
Open-source Identify the console the ROM is from, then use that system's emulator to load it. 
macOS2 apps
OpenEmu
Open-source Polished Mac multi-system emulator - drag the ROM into the library and it picks the right core. 
Linux2 apps
RetroArch
Open-source Load the ROM with the system's core; also the basis of Recalbox/Batocera/Lakka.
Mupen64Plus
Open-source Cross-platform N64 emulator; run the .rom from the command line or a front-end. 
Android1 app
RetroArch (Android)
Open-source Install from the site/Play Store, download the core for the system, and load the .rom to play on a phone/tablet. Technical details
deep spec| Binary encoding | Raw binary - uncompressed, byte-for-byte copy of the original cartridge or chip data |
| Internal structure | System-dependent; no universal header or fixed layout - the binary layout is dictated entirely by the source console or computer |
| Magic bytes / file signature | None; the `.rom` extension carries no fixed identifying signature - identification relies on the emulator or user |
| N64 byte-order variants | Big-endian `.z64` (native MIPS R4300i format), byte-swapped `.v64`, and little-endian `.n64` - emulators convert between them on load |
| MIME type | `application/octet-stream` |
| Typical file size | 256 KB - 64 MB depending on cartridge; most N64 titles range from 8 MB to 64 MB |
| Content coverage | Full game executable code, graphics, audio, and level data exactly as stored on the original ROM chip |
| Compression | None within the file; users commonly archive `.rom` files externally in ZIP or 7z containers |
| Related extension ecosystem | `.z64`, `.n64`, `.v64` (N64); `.smc` / `.sfc` (SNES); `.nes` (NES); `.gba` (GBA); `.gb` (Game Boy) |
| ROM hacking support | The file can be modified with hex editors or patched using IPS/BPS patch utilities such as Floating IPS or beat |
| System identification | Determined by emulator configuration or user selection - not embedded in the `.rom` file itself |
| N64 cartridge header | First 64 bytes encode PI BSD registers, clock rate, boot address, game name (20 bytes), cartridge ID (2 bytes), and country code |
| N64 CRC integrity check | N64 ROMs contain two 32-bit CRC values at offsets 0x10 (CRC1) and 0x14 (CRC2), verified by the console boot ROM at startup |
| Legal context | Personal cartridge dumps are generally permitted in many jurisdictions; distributing or downloading third-party ROMs is typically a copyright violation |
| Released | with console/computer emulation (1990s onward) |
| Specification | emulation.gametechwiki.com |
ROM conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about ROM files.
