Originally Posted by Supamax
I still don't understand a simple thing:
since MAME roms are dumped from the games' chips, wouldn't it be EASY to find a FINAL format to store them?
Why in hell am I forced to download again the rom sets any time?
Once you have a binary dump of all the game ICs, you're done. Every MAME version could use them as they are... or not?
As mentioned, many roms are flagged as bad dumps, even though many of them do still run. People redump these as they find original hardware and so these get replaced in the next version, making the older bad dumped versions of the roms obsolete.
Another reason, and more the main reason for changes to the roms with each revision is the merging of identical rom code into a parent/child/clone rom set structure. Many games used the same underlying cabinets, and many games share a lot of the same roms (using the same libraries and other code on existing roms from other games, and just added a couple of additional roms for the specific game's code). Or other versions of the same games were released in slightly different forms for different countries or markets, and for these most of the roms were identical, so the games are classed as clones of the original and can use the majority of the same roms.
Therefore there isn't really any need to have duplicate copies of the same dumped roms held in the full MAME rom set for all these clones of the same games or games based on the same original game cabinet. These are referred to in MAME as child rom sets. And as new versions of MAME are developed more games that use identical rom sets are found, and so these games become child sets of the original games parent rom sets. So only one of these roms is needed to load and run a large number of games that shared it. This means that the actual rom set file structure is completely changed, and is the biggest reason why games that used to work on an older version of MAME might not work on a newer one. Because the rom set structure has changed.
I hope that made sense.