Paul is right, cylinder and tank vacs ARE the same thing! They are long and narrow and have horizontal airflow. Examples would include the Eurekas pictured in this thread, Electrolux, Filtex, Royal, and Hoover Aerodyne. Canisters are kettle shaped and have vertical airflow. Examples would include Eureka Rotomatic, GE Swiveltop, Hoover Constellation, Lewyt, Filter Queen, and Silver King.