A rotary hammer or SDS drill is usually even bigger and more powerful than a standard hammer drill. It can accommodate masonry drill bits that are several feet long. However, the main difference between the two tools lies in the action. A standard hammer drill adds percussion to the drilling motion, banging the drill forward as it turns. A rotary hammer/SDS drill can use that hammering action on its own, without the drill. So if you fit a chisel or point tool, it becomes a small demolition hammer.