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MAME's purpose is to preserve decades of software history. As electronic technology continues to rush forward, MAME prevents this important "vintage" software from being lost and forgotten. This is achieved by documenting the hardware and how it functions. The source code to MAME serves as this documentation. The fact that the software is usable serves primarily to validate the accuracy of the documentation (how else can you prove that you have recreated the hardware faithfully?). Over time, MAME absorbed the sister-project MESS (Multi Emulator Super System), so MAME now documents a wide variety of (mostly vintage) computers, video game consoles and calculators, in addition to the arcade video games that were its initial focus.
See the [Compiling MAME](http://docs.mamedev.org/initialsetup/compilingmame.html) page on our documentation site for more information, including prerequisites for Mac OS X and popular Linux distributions.
For recent versions of OSX you need to install [Xcode](https://developer.apple.com/xcode/) including command-line tools and [SDL 2.0](https://www.libsdl.org/download-2.0.php).
MAME source code should be viewed and edited with your editor set to use four spaces per tab. Tabs are used for initial indentation of lines, with one tab used per indentation level. Spaces are used for other alignment within a line.
Some parts of the code follow [Allman style](https://en.wikipedia.org/wiki/Indent_style#Allman_style); some parts of the code follow [K&R style](https://en.wikipedia.org/wiki/Indent_style#K.26R_style) -- mostly depending on who wrote the original version. **Above all else, be consistent with what you modify, and keep whitespace changes to a minimum when modifying existing source.** For new code, the majority tends to prefer Allman style, so if you don't care much, use that.
All contributors need to either add a standard header for license info (on new files) or inform us of their wishes regarding which of the following licenses they would like their code to be made available under: the [BSD-3-Clause](http://opensource.org/licenses/BSD-3-Clause) license, the [LGPL-2.1](http://opensource.org/licenses/LGPL-2.1), or the [GPL-2.0](http://opensource.org/licenses/GPL-2.0).
The MAME project as a whole is distributed under the terms of the [GNU General Public License, version 2](http://opensource.org/licenses/GPL-2.0) or later (GPL-2.0+), since it contains code made available under multiple GPL-compatible licenses. A great majority of files (over 90% including core files) are under the [BSD-3-Clause License](http://opensource.org/licenses/BSD-3-Clause) and we would encourage new contributors to distribute files under this license.
