MAME changes how it emulates boards. In version 0.249, Mortal Kombat might have used four ROM chips. In 0.250, the devs discovered the correct dump uses five chips. Your old ROM is now "dirty."
This version saw a massive influx of and various gambling systems. Mame 0.250 Roms
However, in the spirit of preservation, many abandonware and archival sites argue that if a game is no longer commercially available and the copyright holder is defunct, downloading is a gray area. Still, this is not legal advice; proceed with caution. MAME changes how it emulates boards
Non-merged sets are the most user-friendly but also the most space-intensive option. Each game, whether it's a parent or a clone, has its own ZIP file that is 100% complete and independent. This means you can move any game's ZIP file to any MAME setup, and it should run without needing any other files. This is the best choice if you only want a selection of specific games and don't want to manage dependencies. Your old ROM is now "dirty
Keep your arcade ROMs zipped. MAME is designed to read the contents inside .zip or .7z archives directly. Unzipping them breaks the file paths and clutters your directory.
In a non-merged set, every single .zip file is entirely self-contained. The clone file contains all the parent data it needs to run independently.
While MAME 0.250 added the usual slate of obscure gambling machines and LCD handhelds, several major additions stood out, highlighting the frantic race against "bit rot" (the degradation of data on aging chips).