> > So we have to rebuild our roms like the Chd's when they move to v.5 to save space?
> Not only to save space, but I think for newer versions of MAME to recognize them.
Incorrect. Existing ROMs will continue to work fine, and .zip will continue to be preferred on lower-end systems (especially if you have 1 GB or less of RAM). Some CHDs will likely need an update, but it's just an update, not a re-download.