Difference between a full-trailer tractor and a semi-trailer tractor

The front of the car with driving ability is called a tractor, and the car with no traction and driving ability in the back is called a trailer, and the trailer is towed by the tractor. There are two ways to connect the tractor and the trailer: the first is that the front half of the trailer is placed on the traction saddle above the rear section of the tractor, and the bridge behind the tractor bears part of the weight of the trailer, which is the semi-trailer; the second The first type is that the front end of the trailer is connected to the rear end of the tractor. The tractor only provides forward pulling force and drags the trailer, but does not bear the downward weight of the trailer. This is the full trailer.