A full rescan on a complete mame collection takes 90 seconds on my system. ...So I don't see a real need for such an option ;) Besides it would have to do major analyzing of the old and the new datfile to capture all possible changes....so a simple rescan when a datfile has changed is the easiest to do.

Well...hmm....It may be possible to create some hashvalue on the setdata (number of roms, parentname, romnames, etc..) and compare that with the data in the new datfile. If it matches, don't rescan it. The problem: You don't know if something or someone else has changed the data on your harddisk. So you better do a rescan anyway.

Roman Scherzer
ClrMamePro