MAME merged vs split vs non-merged romsets
Use split sets when you keep a complete parent-and-clone collection and want a conventional balance of space and maintainability. Use merged sets when you deliberately manage clones inside each parent container and your frontend understands that layout. Use non-merged sets for a small, portable selection that must minimize parent dependencies, accepting duplication. All three must be built for the exact MAME version and may still require separate BIOS, device, sample, or CHD data.
Do this in order
- 01
Identify the exact MAME or core version, the parent and clone short names you intend to keep, and any BIOS, device, sample, or CHD dependencies.
- 02
Decide whether the library is a complete versioned collection, a parent-focused curated set, or a few portable individual titles.
- 03
Choose split for conventional full-set management, merged for parent-container management, or non-merged for selected clone independence with duplication.
- 04
Build or organize only from your own or explicitly authorized source; never mix files from differently versioned packs.
- 05
Audit one parent, one clone, and one title with a BIOS or CHD using the exact target build and the final Android storage layout.
- 06
Save the build version, layout type, short-name manifest, source evidence, and audit result before importing or updating the larger library.
Decision and diagnostic table
| Layout | Best fit | Main trade-off |
|---|---|---|
| Merged | Complete collections managed by parent family | Clone data lives in the parent container and some frontends handle it poorly |
| Split | Versioned parent-and-clone collections | A clone normally depends on its parent container |
| Non-merged | Small portable selections or independently stored clones | Duplicates shared data and still may need BIOS/device files |
| All three | Exact version-matched legal content | None removes CHD, sample, firmware, or rights requirements |
Layout is not romset version
Merged, split, and non-merged describe where shared parent and clone ROM data is stored. They do not identify the MAME revision whose hashes and dependency graph the files satisfy.
Always record both facts. A perfectly built merged set for an older core can fail current MAME, and converting its containers without correct source data does not update the contents.
Clone independence has a storage cost
A split clone stores only data that differs and relies on its parent. A non-merged clone carries the shared ROM data needed to reduce that parent dependency, which duplicates bytes across several clones.
MAMEdev does not recommend non-merged storage for most large collections. It becomes rational when the maintained selection is small and the operational value of self-contained game archives exceeds duplication.
External dependencies remain external
A 'full non-merged' label used by a third-party tool can still have tool-specific treatment of BIOS and device data. CHDs are separate disk images, and a clone can depend on a parent CHD or other media.
Trust the target build's audit, not a folder label. Test the final Android path because a desktop audit cannot prove that the app can read the copied directory or granted document tree.
Changing set layout does not change copyright or distribution rights. Use your own lawful dumps or creator-authorized files; ArcadeShelf does not recommend complete commercial romsets, BIOS packs, torrents, or download sites.