A top drive is a mechanical device on a drilling rig that provides clockwise torque to the drill string to drill a borehole. It is an alternative to the rotary table and Kelly drive. It is located at the swivel’s place below the traveling block and moves vertically up and down the derrick.
A draw-works is the primary hoisting machinery that is a component of a rotary drilling rig. Its main function is to provide a means of raising and lowering the traveling blocks. The wire-rope drilling line winds on the draw works drum and extends to the crown block and traveling blocks, allowing the drill string to be moved up and down as the drum turns.
The segment of drilling line from the draw-works to the crown block is called the “fast line”. The drilling line then enters the sheaves of the crown block and it makes several passes between the crown block and traveling block pulleys for mechanical advantage. The line then exits the last sheave on the crown block and is fastened to a derrick leg on the other side of the rig floor. This section of drilling line is called the “dead line”