Romcenter

I apologize for the stupid question, but what is the purpose of the supplement dats?

I presume that you are talking about the ones that are for emulators such as Nebula, etc? They create ROM sets that in addition to a good MAME set are all that you need for a particular emulator (i.e. by defining two ROM paths in the emulator; one for MAME ROMs, one for supplement ROMs).

Examples of space used:

A full Nebula set is 2.7GB, supplement is only about 400MB
A full Kawaks set is 2.6GB, supplement is only about 350MB
A full M1 set is 1.6GB, a supplement is only about 400MB

So I have the MAME dats, and the regular dat is complete on my machine. I split merged them. So this means I should make a new directory and fill that with roms from the Split-Merged Supplement? Then I will have the complete set? Why can't they all go into the same dat?

Yes, use the split-merged supplement (the name must match your MAME set). The dats are separate because they are different emulators. It provides more flexibility for people.

When you say they are for different emulators, you mean I need to get an emulator different from MAME in order to play the supplemental roms?

It seems like many of the suplemental roms are the same as the regular roms only named slightly differently. I ran the supplemental dat on my main rom directory and almost all of them were in there. Are there a lot of dupes between the two dats?

Sorry, I guess I still don't understand.

I now think that we are talking at cross purposes. I am starting to think that you are talking about the supplements that come with the MAME dats but I did originally ask you for confirmation that you were talking about the ones for Nebula, RAINE, Kawaks, etc. earlier in this thread.

Right, let me start again because it requires a different answer if you are talking about things like "MAME v0.85 (Split-merged ROM Supplement).dat". Put simply, the MAME supplements list ROM changes between two versions of MAME. In the case of the example I gave above, it includes all ROM changes between MAME v0.84 and MAME v0.85. They are useful for archival purposes and also for people that want multiple versions of MAME playable at once without having several full ROM sets.

If you look inside the ZIP, there are readme's and other text files. For example:

This archive contains dats for ROMs that have been added or updated in the new
release of MAME (v0.85).

There are dats provided for all three set types (fully-merged, split-merged and
non-merged). Make sure you use the dat that matches your ROM collection!

After creating a mini set of ROMs with these dats you can use them in addition
to an existing MAME v0.84 set without any problems for MAME v0.85.

Logiqx, http://www.logiqx.com/

Logiqx

Then what are the "MAME Changes" dats?

Thanks for putting up with my ignorance

Changes are complete zips (i.e. for added or changed ZIPs). Supplements are not necessarily complete ZIPs (they contain the minimum number of ROMs necessary for an update).

For example, if one ROM is added to a game then the supplement will list just the one ROM but the changes will list every ROM in that game.

Changes also has a readme:

This archive contains dats for ROMs that have been added or updated in the new
release of MAME (v0.86).

There are dats provided for all three set types (fully-merged, split-merged and
non-merged). Make sure you use the dat that matches your ROM collection!

After creating a mini set of ROMs using these dats you can copy them over an
existing MAME v0.85 set to create a _perfect_ MAME v0.86 set.