RDA’s (Rebuildable Dripping Atomizers) aka Drippers, were the original way people were able to Sub Ohm. These are usually smaller devices than tanks that attach to Mechanical or Box Mods. They contain a deck where coils are built and attached using a screwdriver and wicked with cotton. Users drip a small amount of juice directly on to the coils and wick before every few puffs.
RTA’s (Rebuildable Tank Atomizers) are for people who want to build coils but do not want to drip. RTA’s are essentially clearomizers that require the user to build the actual coil(s) inside. This gives them freedom to create a coil that will give them the exact type of vape they want. Recently many RTA’s have been geared towards the Sub Ohm vaper with the appropriate airflow options.