So you want to keep the old ones on dvd and the new ones e.g. on harddisk and want to do a scan?

Well...easy...Let one rompath point to the dvd, keep that as the 1st rompath and disable scanner->advanced->use optimized rompath scan (or whatever) since that will dynamically alter the rompath order (if enabled).

If you have more than one dvd (which is rather likely), you have to insert disk 1, do a SCAN, insert disk 2, do a FASTSCAN, insert disk 3, do a FASTSCAN and so on...

..or stick with the diffdatfiles which become available for each new mame version...so you only keep the current updated ones on your harddisk. Take a look at mamediff which can also create such dats for you.

Roman Scherzer
ClrMamePro