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4. About ROMS

4.1 What is a ROM?

ROM really stands for (R)ead (O)nly (M)emory. However in emulation terms, ROM means simply the data contained inside the ROM-chips of the games PCB (Printed Circuitry Board.) The data inside these ROM-chips is "dumped" (copied) to an ordinary binary computer file. So, when you are running MAME with the ROMs from a game, then you're actually playing exactly the same game that you played, down at your local arcade.

4.2 What is a sample? Why do I need it?

A Sample is an audio "sample" from the original arcade games. This is so MAME can duplicate audio on games that had audio hardware that is difficult or impossible to emulate.

For samples see

4.3 What is a ROM set?

Mame allows for different styles of 'sets' or 'where to place ROMS'

At the basic level, a ROM is a chip on a PCB (printed Circuit board) This can be transfered to a file (called a ROM- to maintain consistancy) An arcade game can consist of several ROMs on one PCB. ON the PC side, as a result, a Game can require several ROM files.

Due to the size involved, mame needs these files collected together in ZIP files (compressed files using Winzip or similar)

But, in mame, there are several games are are similar, but vary slightly. These generally result in the changing on a single ROM chip on the PCB (hence also a change of ROM filename) As a result. Mame is able to work in a child / parent basis.. where is it organised through mame that a 'child' set can also obtain needed rom files from the 'parent' zip file.

As a result of this there exists the possibilty for 3 different types of 'SETs'

Not Merged Sets - These invole EVERY romfile being stored in EVERY zipfile needed for a given game... This result its duplicity for several files & is very wasteful in disk space.

Split sets - This create a number of Zip files, where the 'parent' ZIP file contains all the shared files the the 'child' needs. This also creates Zipfiles for each child ZIPfile that contains just the Rom Files that the child requires; but are not required by the parent. (advantages, If missing a set or a rom, it is generally smaller & easier to locate... Most people use this system)

Merged sets - This idea removes the child / parent idea. & allows for only parent Zip files. This singular Zip file contains all the roms required for every child based game. (advantages : less Zip files required.)

4.4 What are split/merged/parent ROMs?

A "Parent" version is simply the most final bug-free / widest released version of a given game, other versions of that game are then said to be clones of the parent version.

As MAME will often emulate several different version of the same game, and as these different ROM-sets often have many files in common, MAME allows you to save space by first searching for the required files in the parent ROM-file.

This allows you to either throw all parts from all the different versions together in the parent zip-file ("merged") or to keep just those parts of a clone that are not duplicated in the parent file in their own zip-file ("split") or simply to have all necessary parts in each and every zip-file ("un-merged").

4.5 Can I get a Virus from a ROM?

No, a virus *CANNOT* infect your computer from a ROM file.

However, if your computer *already* is infected by a virus, then that virus may try and attach itself to a ROM file just like it may attach itself to *any* other file on your computer. This will simply ruin the ROM-file.

Far more common are "False positives", where your Anti-virus program says that a specific ROM-file contains a virus, though it in reality doesn't.

4.6 What does 'No good dump known' or 'ROM needs redump' mean?

When the version of MAME you are using was compiled, the MAME team didn't know of a good dump of that specific ROM. A good version of the ROM may pop up later, but remember that the message will still be displayed until you switch to a newer version of MAME, compiled with the correct information about the ROM.

(Think of it, as a request for a good dump, from the MAME people to arcade board owners.)

4.7 Why does most games display garbage, when I start them?

It isn't really garbage, it is the original boot-up sequence. Just like when you turn on your computer, it shows a lot of different screens while booting, so does an arcade game show this, when it is turned on. Depending on the speed of your computer and the length of the boot-up sequence, it may take up to thirty seconds before the arcade game is ready to accept coins.

4.8 Can I download all the MAME ROMs in one big file?

No. Such a file would be well above 10 GiB of data, and it would have to be deleted and an updated version would have to be uploaded, each and every time a new version of MAME is released. (See the next question for an alternative.)

Yes. Bittorrent is your friend. (see Where can I find ROMs?)

4.9 What are .chd files? What is a CHD?

CHD stands for "(C)ompressed (H)unks of (D)ata" - the odd acronym owes it self to the fact that the format was originally "(C)ompressed (H)ard (D)isk" but has subsequently be expanded to fit a variety of media storage (CD-ROM, etc.). These files are not technically ROM files, since they contain a drive image, rather than a ROM chip image. Some games had disk drives in them with extra data, large hard disks, or CDs are substantially cheaper than large ROM chips. Because of this, CHD files will typically be much larger than any ROM files you have. Please see the "Technical Information" section for more detailed information.

4.10 What do I do with these ROM files? Should they be uncompressed?

You do not have to decompress ROM files for MAME to use them. For the sake of your hard disk space don't do it. Simply put the zip files into your ROM directory and MAME will handle the rest. CHD files need to go into a sub-directory of your ROM directory, for example:
Lets say your ROMS directory is '/mame/roms'. In order to run "Area 51" you would have to have the file '' in '/mame/roms', and you would have to have 'area51.chd' in the folder '/mame/roms/area51'. The complete listing would be:

/mame/roms/ /mame/roms/area51/area51.chd

Although the majority of games follow this "rule", there are some exceptions, most notably the "Beatmania" series of games. For these games the CHD file does not have the same name as the games ROM. For example the game "Crypt Killer" uses a ROM file called "" and a CHD file called "420uaa04.chd", this CHD would be put in a directory called "cryptklr". Please refer to one of the CHD information links given in the previous question for a complete list of games and thier CHD files.

It seems that some derivative versions of MAME may require .chd files to be in an "image" directory. Word has it that AdvanceMAME defaults this to a directory called "image". In this case you can either change the image directory to your ROM directory or put the .chd files in the image directory in the same manor as described above. Refer to the documentation for the build you are using for directions.

4.11 What are BIOS ROMs?

I have downloaded a {fill in system name} game, now why doesn't it run?

BIOS ROMs are just like game ROMs, only they don't have a game in them. Think of them like a parent ROM for all the games on a given system if you will. This is a list of all the systems that MAME support, which require a BIOS. The BIOS ROM name is in parenthesis. BIOS ROMs go in the same folder as all other ROMs.

The systems that require BIOS files are (as of MAME 0.79):

System BIOS files are treated no differently than other parent ROMs, you don't have to do anything special other than place the appropriate file in your ROM directory.

4.12 Where can I find ROMs? is NOT a binary newsgroup. Do not ask to have ROM files posted to Asking for ROMs in will be a sure sign that you DID NOT READ THE FAQ. It is also the quickest way to get in someones killfile. Because you are reading the FAQ you can use the following means to attempt to get ROMs.

Your options are:


There are quite a few websites that have some or occasionally even all of the MAME ROMs available for download. Try lurking a bit in to look for announcements of new/active websites or FTP-servers, or you could take a look here:


If your NSP carries them, then you should definitely try the following binary newsgroups (Try posting a polite request, or simply wait for the next mass-post...):


For a *FREE* MAME ROM set on CD/DVD there are several people who would be glad to help you.


There are various p2p filesharing utilities out there, some of these might also be useful for finding MAME ROMs.

Bit Torrent

Try for some trackers. I have not personally tried this site or any of the trackers listed.


If you only need a few smaller ROMs or partial ROMs you might try to post a [MAIL-REQ] post in, and hopefully someone will e-mail them to you.
NOTE: Some (usually newer) ROMs are positively HUGE, so please make sure that your e-mail-box can handle these before asking, okay?
NOTE: Do *NOT* post any binaries in in reply to a [MAIL-REQ], but please *DO* post a message that you have filled the request, to stop others from doing the same.

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