Question regarding rollback rom sets

[Extreme8]

So far I've discovered the wonderful world of compiling my own Mame, and managed to master clrmame pro enough to generate full romsets for whichever older mame versions I desire. I have my samples together and have a fairly full set.

My question is about how older romsets handle CHD's. Do these need to be rolledback as well, or does the current version of the CHD's work with older mame versions. I expect not, but I haven't seen a CHD rollback set so I'm  curious.

If anyone can shed some light on the subject it would be appreciated.

[Howard_Casto]

Telling us what version you want to roll-back to might help. 

Mame chds, in general are rather impossible to "roll back" as they are a single file.  Generally speaking though, they don't change that much.  I think aaron has included utilities to upgrade older chds, but I don't know about the other way around.

[Tiger-Heli]

0.77u1 is when the CHD format was changed.

Update files from the previous format are here: http://www.mametitles.com/chd.html, but I don't know of a "rollback" utility.

[um3k]

Even after 0.77u1, some of the CHDs have changed content slightly (some Gauntlet CHDs around 0.102) or been removed from MAME (CPS2 fighters from 0.111).  If you wanted to roll back to before those versions and play those particular games you would need the appropriate version of the CHD.   A CHD "rollback" set would probably contain the entire old CHD, which you would use instead of the more recent CHD.  It's not like roms, where just the removed/changed roms are in the rollback and you use CMP to scan them.