This is the most critical part of the filename. The .part23 suffix indicates that this is .
Version 0.139u1 is a "sweet spot" for emulation performance on mobile devices and low-power hardware like the Raspberry Pi Device Support
Because PD also supported "FTP dumping" for users with bad internet. You could download parts 1-10 via FTP, pause, resume later with parts 11-20, and finally torrent the rest. RAR splitting allowed for resumeable downloads in an era before modern browsers supported large file resuming.
Why does this matter? In the emulation world, MAME updates are notorious for breaking compatibility. A ROM (game file) that worked perfectly on version 0.139 may not work on 0.200, and vice versa. Version 0.139u1 was released in . This means the file in question is rooted in the early 2010s emulation scene, a time when downloading complete ROM sets via torrents and Usenet was at its peak.
It looks like you’re asking for a about a specific file: MAME-Plus-v0.139u1.part23.rar
