MAME is a computer software program for personal computers designed to faithfully and precisely emulate as many arcade games as possible, with the intent of preserving gaming history and preventing vintage games from being lost or forgotten. The name is an acronym for Multiple Arcade Machine Emulator.

MAME has been ported to many different platforms. The X11 port for Unix-like systems is named XMAME. The Mac OS X port is named MacMAME.

According to the official MAME web site, the first public MAME release (0.1) was on February 5, 1997, by Nicola Salmoria. As of version 0.108 (actually the 152nd proper release), released August 20, 2006, MAME now supports 3349 unique games and 6216 actual ROM sets (each game may just have the original or have one or more clones as well - see below) and is growing all the time. However, not all of the games in MAME are playable; 710 ROM sets are marked as not working in the current version, and 26 of the 6216 sets are not actual games but BIOS ROM sets.

How MAME works

MAME contains several components: a CPU emulator which duplicates the behavior of the CPUs of many original arcade machines; an input emulator which maps arcade buttons, joysticks, and other controls to PC keyboards, joysticks and other devices; and an emulator for the arcade game display and sound equipment. The only thing missing from MAME is the ROM image, which is the program from the original arcade game which made the game run. When MAME is run, it is running the original game from several years ago - just on different hardware.

Emulation philosophy

The stated aim of the project is to document hardware, and so MAME takes a somewhat purist view of emulation, prohibiting programming hacks that might make a game run improperly or run faster at the expense of emulation accuracy (see UltraHLE, a project aimed to run games at a playable speed). In MAME every emulated component is replicated down to the smallest level of individual registers and instructions. Consequently, MAME emulation is very accurate (in many cases pixel- and sample-accurate), but system requirements can be high. Since MAME runs mostly older games, a large majority of the games run well on a 2 GHz PC. More modern arcade machines are based around fast pipelined RISC processors, math DSPs, and other devices which are difficult to emulate efficiently. These systems may not run quickly even on the most modern systems available; some working games have been estimated to require a 10 GHz processor to run at full speed.

The MAME team has not diverged from this purist philosophy to take advantage of 3D hardware available on PCs today. It is a common but incorrect assumption that performance problems are due to some games` use of 3D graphics. However, even with graphics disabled, games using RISC processors and other modern hardware are not emulated any faster. Thus taking advantage of 3D hardware would not speed these games up significantly. In addition, using 3D hardware would make it difficult to guarantee identical output between different brands of cards, or even revisions of drivers on the same card, which goes against the MAME philosophy. Consistency of output across platforms is very important to the MAME team.

MAME Releases

There are several types of MAME release depending on how frequently users wish to update and the level of code maturity each user feels comfortable running:

The major releases of MAME occur approximately once a month. These releases are given a version number, e.g. 0.99. The Unix numbering scheme is used, i.e. the version after 0.99 is 0.100, which seems counter-intuitive to some. These major releases are the most mature and least frequent ones so are aimed at the average computer user who wants to try MAME. An executable version for Windows & DOS is released from the MAME Home Page.
Smaller, incremental releases are released between major releases. These releases are denoted by a `u` number after the version number of the previous major release, e.g. 0.99u1 is the first development release after major version 0.99. There are usually about 5 new `u` releases in between major releases. These minor releases are not intended for average MAME users. Instead, they are aimed at people who take a close interest in MAME development and have access to compiler tools. As such, these minor releases are not made officially available as executables. They are available only as diffs against the MAME source code.
For those users who must keep up with the absolute daily goings-on with MAME development, the MAME source code is kept on the Mess.org CVS server and may be downloaded at will by any member of the public. This is intended only for those who have access to compiler tools and feel comfortable building software from source code.

ROM images

In most arcade machines, the data (consisting of the game program, graphics, sounds, etc.) is stored in read-only memory chips (hence the name `ROM`), although other devices such as cassettes, floppy disks, hard disks, and compact discs are also used. These devices can be read in a process called `dumping` to create computer files containing the same data; these files are often generically called `ROM images` or `ROMs` no matter what kind of device they originally came from. To play a particular game, MAME requires a set of files (called a ROM set) containing all the data from the original machine, however MAME itself does not include any of these files.

MAME handles these data files in two ways: CHD (Compressed Hunks of Data) files hold the contents of hard disks or compact discs, and all the other types of game data are stored in ZIP archives, one for each game.

There are three types of ROM sets:

Original game ROM sets (`parent`). These are the games which the MAME development team has decided are the `original` versions of each game. Except for the files contained in BIOS ROMs (if needed; see below), the ROM files for these games contain everything those games need to run. The `original` set is generally defined as the most recent revision of the game, and if multiple regional versions are available, the `World` or US revision.
Clone ROM sets, which are different versions or variants of the originals (for example, Street Fighter II Turbo is considered a variant of Street Fighter II Champion Edition).
BIOS ROM sets, which are the ROMs in common between all games on various standardized arcade systems (e.g. Neo-Geo). They basically `boot` the hardware, then allow the regular game software to take over.

Rom Naming:

MacMAME under Mac OS X running Progear.A single supported game is usually refered to as a `Romset`, as for the majority of cases each game will consist of multiple `ROM` files, each of which represents a single device (usually ROM, but sometimes other devices such as PALs)

The MAME developers assign each Romset an 8-letter name for identification as well as a description associated with that 8-letter name.

hyperpac `Hyper Pacman`

MAME expects to find all the ROM images required for the game `Hyper Pacman` in a folder, or ZIP file called hyperpac(.zip) For games which are considered clones, for example

hyperpcb `Hyper Pacman (bootleg)`

MAME will look in both the parent folder (hyperpac) and the clone folder (hyperpcb) for the files.

Individual ROM files are, where possible, named after labels found on the ROM chips, and the position they are located on the board in the format `label.position`. Sega for example use a standard labeling scheme for all the ROMs found on their arcade boards giving each unique ROM chip a unique label. `mpr12380.b2` is a ROM from the Golden Axe romset. This implies that the rom was labeled `mpr12380` and located in position `b2` on the PCB. By using such a naming scheme it makes it easy to use MAME to identify, and often help repair, non-working PCBs.

The 8-letter identification tags are less standardized and usually left to the discretion of individual developers, likewise the descriptive long names, although some standards do exist, again often following naming conventions set by the original game manufacturers. Taking Konami`s Sunset Riders as an example

ssriders `Sunset Riders (4 Players ver EAC)`
ssrdrebd `Sunset Riders (2 Players ver EBD)`
ssrdrebc `Sunset Riders (2 Players ver EBC)`
ssrdruda `Sunset Riders (4 Players ver UDA)`
ssrdreaa `Sunset Riders (4 Players ver EAA)`
ssrdruac `Sunset Riders (4 Players ver UAC)`
ssrdrubc `Sunset Riders (2 Players ver UBC)`
ssrdrabd `Sunset Riders (2 Players ver ABD)`
ssrdradd `Sunset Riders (4 Players ver ADD)`
ssrdrjbd `Sunset Riders (2 Players ver JBD)`

Konami gave each revision of their later (mid 90s onwards) games a very specific and clearly visible version number. As these represent an easy way to identify each version of the game, including the region in which it was available and the revision of the code, MAME uses this information to identify each set. UAA is American revision A, while ABD is Asian revision D.

For companies where it is less clear sets are often simply labeled as `(set 1)` and `(set 2)`. Unreleased games as labeled as `(Prototype)` and non-original versions of games are labaled as `(Bootleg)`

Obtaining Roms:

Roms can be obtained through a number of methods.

1. Legally, from www.mamedev.org. For Three ROM sets, Gridlee, Robby Roto, and Alien Arena the game`s copyright holders have given permission for them to be freely distributed for non-commercial use.
2. By using an EPROM reader, to read the ROMs yourself from your Arcade PCB.
3. Illegally usually through download services or otherwise.

For more information on the legality of ROMs see the main ROM Image article.

Front ends

Emuloader being used with MAME, Emuloader is a popular MAME Front End for use on Windows.Although the main MAME program is only made available as a command-line application for Windows and Linux, there are several popular front ends, such as GXMame[2] for Linux, which allow MAME to be launched from a more familiar, graphical environment as well as providing facilities such as auditing ROMs. MAME32 for Windows (not a front end, but a full port) also offers this functionality.

Additionally, the front ends make available more information about the games themselves, contributing significantly to the experience, such as history information and images of the arcade cabinets.

Some frontends have the sole purpose to launch games and hide the operating system. These frontends are generally used in MAME arcade cabinets, to enhance the illusion that the cabinet is a real arcade machine.

Legal status of MAME

Owning and distributing MAME itself is legal in the US, as it is merely an emulator. Some companies (notably Sony) have attempted in court to prevent emulators from being sold, but they have been ultimately unsuccessful. As yet, no legal action has been brought against the MAME team.

The situation regarding ROM images of games is less clear-cut. Most if not all arcade games are still covered by copyright.

Some copyright holders have been indecisive regarding making licensed MAME ROMs available to the public. For example, in 2003 Atari made MAME-compatible ROMs for 27 of its arcade games available through the internet site Star ROMs. However, a status check in March 2006 revealed a reversal of that decision, and the ROMs are no longer being sold there.

Other copyright holders have released games which are no longer commercially viable free of charge to the public. Games including Gridlee and Robby Roto have been released by their copyright holders under non-commercial licenses. These games may be downloaded legally from the official MAME web site.

However, the majority of games emulated in MAME at this time are copyrighted but no longer commercially available in any form. The legality of distributing or downloading such games depends greatly upon the laws in each country. Many national copyright laws include language which limits offenses to those which cause material harm to copyright holders. An argument could be made that where a game is no longer being manufactured or sold, this could not be the case.

A peculiar legal situation exists with regard to games which are covered by copyright but where there no longer exists a copyright holder. Such games are termed orphan works. They are covered by copyright but, since they have no legal owner, do not make money for anybody. Copyright reformers such as Lawrence Lessig believe that such works no longer have a reason to be copyrighted and should be in the public domain. The United States Copyright Office is currently seeking comments on this issue.

MAME license

While MAME is available at no cost, including its source code, it is not open-source software or free software because commercial use and redistribution are prohibited. That is, its license does not meet the conditions of the Open Source Definition, nor is it `free software` as defined by the Free Software Foundation.

In particular, MAME may be redistributed in source or binary form, either modified or unmodified, but: `Redistributions may not be sold, nor may they be used in a commercial product or activity.` Also, redistributions of modified versions (derivative works) must include the complete corresponding source code (similar to a copyleft).

There exist, however, a number of unlicensed builds, including multiplayer builds that support the Kaillera server protocol, or others that add newer games.