Surface computers are large-screen displays that support direct interaction via touch or gesture. They may be horizontal (built into furniture such as a tabletop), or vertical (wall-mounted or free-standing). They incorporate the elements of multitouch interactions found in handheld devices but often recognize multiple users, allowing collaborative use. Size is constrained by the ability to physically reach across the surface. Larger displays usually support a gestural interface, where the user does not need to physically touch the surface.