if i am correct then dds 120's, are 120 minutes long?
Nope. DDS and DAT (audio) tapes use different units:
DAT (audio) = minutesObviously, minutes are minutes - no confusion here.
DDS = metersTo convert meters to minutes, multiply by 2. So...a 120m DDS tape = 120 meters x2 = 240 minutes.
However, you should
not use DDS 120m tapes in your DAT deck - audio DAT decks are not made to handle tapes of that length and they'll
wear out your deck faster if they work at all. In general, DDS 60m (x2 = 120min) tapes are the way to go, with an occasional DDS 90m (x2 = 180min) tape if there's a chance the sets will run longer than 120 minutes.