A milling machine is a machine tool used to machine solid materials into a wide variety of sizes and shapes. The precision parts manufactured are generally used as components of other machines, retail items, or assemblies. Milling machines are often classed in two basic forms, horizontal and vertical. This refers to the orientation of the main spindle. Both types range in size from small, bench-mounted devices to room-sized machines. Unlike a drill press, which holds the workpiece stationary as the drill moves axially to penetrate the material. Milling machines also move the workpiece radially against the rotating milling cutter, which cuts on its sides as well as its tip. Milling machines may be manually operated, mechanically automated, or digitally automated via computer numerical control (CNC).