How are the IRA and Ulster Volunteers different?

The original IRA no longer exists. The one you're speaking of is the PIRA(provisional). Only real difference is anti-catholic vs anti-protestant between Ulster and the PIRA. Both are considered paramilitary and terrorist organizations. The true IRA was founded after the failed Easter Rising in1916 and paved the way to Ireland becoming free. Although it split from the founded Irish free state and started the Irish civil war. The PIRA was officially founded after in1969 after Ireland had become its own country with the goal of "freeing" N. Ireland from the UK. The Ulster Volunteers came about as a retaliation to the PIRAs attacks true issue being catholics vs protestants. Although both are fought on different sides of "The Troubles" neither ones acts were sactioned by Ireland or the UK which makes them, as stated earlier, paramilitary and terrorist groups as both have killed hundreds of innocent civilians. ERIN GO BRAUGH