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A ROM image, or simply ROM, is a computer file which contains a copy of the data from a read-only memory chip, often from a video game cartridge, a computer's firmware, or from an arcade game's main board. The term is frequently used in the context of emulation, whereby older games or computer firmware are copied to ROM files on modern computers and can, using a piece of software known as an emulator, be run on the newer computer.

ROM images are also used when developing for embedded computers. Software which is being developed for embedded computers is often written to ROM files for testing on a standard computer before it is written to a ROM chip for use in the embedded system. At present, this article deals mainly with the use of ROM in relation to emulation.


ROM chips, while still in use, have been replaced in many instances by optical media such as CD-ROMs and DVD-ROMs, magnetic media such as hard disks and magnetic tapes and, more recently, Flash Memory chips. However, the term ROM is commonly also used to cover many of these newer media so, for instance, a computer game copied from a magnetic tape may also be incorrectly referred to as a ROM. The correct names for tape and disk 'roms' are Tape image and Disk image respectively. Images copied from optical media are also called ISO images, after one of the standard file systems for optical media, ISO 9660. Many ROMs used by emulators, and particularly console emulators, are not true images of the ROM chips in the cartridge. They are often modified to allow easier functionality in emulators through methods such as combining the images from multiple ROM chips.


Dumping ROMs and creating images

ROMs can be copied from the read-only memory chips found in cartridge-based games and many arcade machines using a dedicated device in a process known as dumping. For most common home video game systems, these devices are widely available. Dumping ROMs from arcade machines, which in fact are highly customized PCBs, often requires individual setups for each machine along with a large amount of expertise.

Creating images from other media is often considerably easier and can often be performed with off-the-shelf hardware. For example, the creation of tape images from games stored on magnetic tapes (from, for example, the Sinclair ZX80 computer) generally involves simply playing the magnetic tape using a standard audio tape player connected to the line-in of a PC sound card. This is then recorded to an audio file and transformed into a tape image file using another program. Likewise, many CD and DVD games may be copied using a standard PC CD/DVD drive.

Digital preservation

The lifespan of digital media is rarely great. While black-and-white photographs may survive for a century or more, many digital media can become unreadable after only 10 years. This is beginning to become a problem as early computer systems may be presently fifty or sixty years old while early home video consoles may be almost thirty years old. Due to this aging, there is a significant worry that many early computer and video games may not survive without being transferred to new media. So, those with an interest in preservation are actively seeking older arcade and video games and attempting to dump them to ROMs. When stored on standardized media such as CD-ROMs and DVD-ROMs, they can be copied to future media with significantly reduced effort.

The trend towards mass digital distribution of ROMs images, while potentially damaging to copyright holders, may also have a positive effect on preservation. While over time many original copies of older games may deteriorate, be broken or thrown away, a copy in ROM or Image form may be distributed throughout the world, allowing games which would otherwise have been lost a greater chance of survival.

Copy prevention mechanisms

While ROM images are often used as a means of preserving the history of computer games, they are also often used to facilitate the unauthorized copying and redistribution of modern games. Seeing this as potentially reducing sales of their products, many game companies have incorporated features into newer games which are designed to prevent copying, while still allowing the original game to be played. For instance, the Nintendo GameCube used non-standard 8 cm DVD-like optical media which for a long time prevented games from being copied to PCs. It was not until a security hole was found in Phantasy Star Online Episode I & II that GameCube games could be successfully copied to a PC, using the Gamecube itself to read the discs.

SNK also employed a protection on their Neo Geo games starting with The King of Fighters in 1999 which used an encryption algorithm on the graphics ROMs which prevented them from being played in an emulator. Many thought that this would mark the end of NeoGeo emulation. However, as early as 2000, crackers found a way to decrypt and dump the ROMs successfully, making them playable once again in any NeoGeo emulator.

Another company which used to protect their arcade games was Capcom which is known for its CPS-2 arcade board. This contained a heavy copy protection algorithm which was not broken until 7 years after the system's release in 1993. The original crack by the CPS2Shock Team was not a true emulation of the protection because it used XOR tables to trick the game into decrypting and play in an emulator. Their stated intent was to wait until CPS-2 games were no longer profitable to release the decryption method (three years after the last game release). The full decryption algorithm was cracked in 2007 by Nicola Salmoria, Andreas Naive and Charles MacDonald of the MAME development team.

Another copy protection technique used in cartridge-games was to have the game attempt to write to ROM. On an authentic cartridge this would fail or cause an exception, however, emulators would often allow the write to succeed. Pirate cartridges also often used writable chips instead of ROM. By reading the value back to see whether the write succeeded, the game could tell whether it was running from an authentic cartridge. Alternatively, the game may simply attempt to overwrite critical program instructions, which if successful renders it unplayable.

Some games, such as Game Boy games, also had other hardware such as memory bank controllers connected to the cartridge bus. The game would send data to this hardware by attempting to write it to specific areas of ROM; thus, if the ROM were writable, this process would corrupt data.

Capcom's latest arcade board is the CPS-3. This was resistant to emulation attempts until June 2007, when the encryption method was reverse-engineered by Andreas Naive. It is currently implemented by MAME and a variant of the CPS-2 emulator Nebula.

Hobbyist collectors

Like many other items such as stamps and coins, ROMs are also collected by many fans. The motives for doing this vary from a desire to preserve the history of computer and video games to obsessive collectors. Those who desire to collect all ROMs have been derided by the MAME developers as PokéROMs, in a reference to the obsolete Pokémon catchphrase "gotta catch 'em all." PokéROM can also refer to "Pocket ROMs" as Pokémon refers to "Pocket Monsters"; since the advent of the GP2X, PSP, DS and other portable handheld gaming machines capable of emulation and even with some Cellphones, people can now have an entire library of old games in their "pocket".

Given the desire by many people to collect ROMs, there are many projects on the internet which dump ROMs, catalogue them or provide tools to verify the correctness and completeness of ROM collections. However, it is illegal to download copyrighted ROMs from the internet. Most old games are copyrighted.

Internet distribution

The trading of ROMs over the Internet is widespread. Many methods are used for such distribution, including:

Although the large size of games for recent consoles makes the distribution of more than one game at a time impractical, it is often the case for older consoles that many thousands of games can be distributed together as a collection. Larger games are often distributed one by one.

Hacks and fan translations

Once games have been made available in ROM format, it is possible for users to make modifications. This may take the form of altering graphics, changing game levels, tweaking difficulty factor, or even translation into a language for which a game was not originally made available. Hack can often take humorous forms, as is the case with a hack of the NES version of Mario Bros., entitled Afro Mario Brothers, which features the famous brothers wearing Afro haircut. The Metroid Redesign mod is a hack of Super Metroid that revamps the game and adds new objectives.

A large scene has developed to translate games into other languages. Many games receive a release in one part of the world, but not in another. For example, many computer role-playing games released in Japanmarker go unreleased in the West. A group of fan translator will often translate the game themselves to meet obvious demand for titles. For example, the 1995 game Tales of Phantasia was only officially released in Japan; DeJap Translations translated the game's on-screen text into English in 2001. Further to this, a project called Vocals of Phantasia was begun to translate the actual speech from the game. An official English version was not released until March 2006, some five years after the text translation was released. Another example was that of Mother 3, a Japan-only sequel to the cult-favorite Earthbound. In spite of massive fan response and several petitions for an English translation, the only response from Nintendo was that Mother 3 would be translated and released in Europe, which it never was. Instead, the fan website undertook a massive translation project and released the translated version of Mother 3 in October, 2008. The translation was praised by fans and even employees from Nintendo, Square Enix, and other industry professionals.

The Japanese N64 game Dōbutsu no Mori (Animal Forest) has also been translated into English. The game was originally only released on N64 in Japan, but it was ported to GameCube and renamed Animal Crossing.

Hacks may range from simple tweaks such as graphic fixes and cheats, to full-blown redesigns of the game, in effect creating an entirely new game using the original as a base.

One of the oldest games that has an active ROM hacking scene to this day is Super Mario Bros.

Legal status

ROMs themselves are not illegal per se. This section gives a general discussion of the legal status of ROMs as regards the various uses to which they may be put, though this should not be construed as legal advice.

Private ownership

In some countries, it is legal for an individual to personally make backup copies of a game they own. Individuals may make backup copies for various reasons, perhaps as insurance against losing the game or as redundancy in the event that the original game's medium becomes unreadable. See the section on ROMs and Preservation.

However, in the U.S. it has been illegal since 1983 for a user to create their own backups of video game ROMs onto other cartridges. This was decided in the court case of Atari v. JS&A. JS&A manufactured a "game backup" device that allowed users to dump their Atari ROMs onto a blank cartridge. JS&A argued that the archival rule allowed for this. The court disagreed, noting that ROM media was not subject to the same volatility as magnetic media (for which the law was created). Thus, not being so relatively vulnerable, ROMs were not applicable under section 17 USC 117(a)(2).

Some games companies, such as Nintendo, print warnings inside their game manuals that they do not allow users to make backup or archival copies. Whether or not these warnings in this specific form can be considered valid contracts is legally questionable. For an overview of relevant issues, see user agreement , shrink wrap contract, clickwrap, Fair Use, Fair Dealing and DMCA.

Official licenses

It is, of course, legal to purchase a ROM image which has been licensed to you by the rights holder. For example, Atari once made a number of their original arcade games available in ROM format which is compatible with the MAME emulator through the online ROM retailer Star ROMs. Nintendo provides a service on their 7th generation console, the Wii, that allows players to purchase old games from various systems, such as the NES, which will download a ROM image and emulator upon purchase (see Virtual Console). This is similar to the Playstation Store re-releases of games for the original Playstation for the Playstation 3 and Playstation Portable, and the Xbox Live Arcade's re-release of many old video games such as the original Sonic the Hedgehog for the Xbox 360.

The vast majority of computer and video games from the history of such games are no longer manufactured. As such, the copyright holders of some games have offered free licenses to those games, often on the condition that they be used for non-commercial purposes only. For example, fourteen of the games emulated in MAME, including Gridlee and Robby Roto, have been made available under such licenses and are distributed by the MAME project.

Unlicensed ROMs

While some games which no longer make any profit fit into the category above, the vast majority are no longer available in any form. The legality of obtaining such games varies from country to country. Some countries have special exceptions in copyright laws or case law which permit (or discourage less) copying when an item is not available for legal purchase or when the copying is for non-commercial or research purposes, while other countries may make such practises firmly illegal. There is often a distinction drawn between distribution and downloading, with distribution being seen as the greater offence.

Commercial distribution of copyrighted games without the consent of the copyright holder is generally illegal in almost all countries, with those who take part in such activities being liable for both criminal and civil penalties. Online auction sites such as eBay have sometimes been used by sellers to sell unauthorised copies of games which are advertised as legitimate copies. Such sellers, in addition to violating copyright laws, may also be prosecuted for fraud or false advertising.


It is often the case that games still under copyright protection are no longer sold or marketed by their copyright holders. This may be due to the perceived lack of demand or for other reasons. Some hobbyists engaged in ROM trading claim that such games should be deemed abandoned by their respective copyright holders so that the games, classed as abandonware, can be freely traded. However, the copyright laws of most countries, including all signatories of the Berne Convention, grant copyright holders the exclusive right to distribute, or not distribute, a work until such time as the copyright expires under law or is granted to the public domain by the copyright holder.

Legal enforcement

There have been few convictions and lawsuits related to ROM trading. Criminal convictions tend to be related to high-profile warez groups which trade combinations of recent films and computer games. In contrast, the ROM scene tends to concentrate mostly on older games. Given the lack of continuing profit from most older games, the grievances of games companies rarely exceed sending a cease and desist letter which demands that the recipient stop distributing the copyrighted works in question.


  1. CPS2Shock (2001-jan-07) The Future Intent of CPS2shock, accessed 2007-aug-10

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