A skid loader or skid steer loader is a rigid frame, engine-powered machine with lift arms used to attach a wide variety of labor-saving tools or attachments. Though sometimes they are equipped with tracks, skid-steer loaders are typically four-wheel drive vehicles with the left-side drive wheels independent of the right-side drive wheels. By having each side independent of the other, wheel speed and direction of rotation of the wheels determine the direction the loader will turn. Skid steer loaders are capable of zero-radius, "pirouette" turning, which makes them extremely maneuverable and valuable for applications that require a compact, agile loader. Unlike in a conventional front loader, the lift arms in these machines are alongside the driver with the pivot points behind the driver's shoulders. Because of the operator's proximity to moving booms, early skid loaders were not as safe as conventional front loaders, particularly during entry and exit of the operator. Modern skid loaders have fully-enclosed cabs and other features to protect the operator. Like other front loaders, it can push material from one location to another, carry material in its bucket or load material into a truck or trailer.