In a quest to build a thinner device, Lenovo has finally abandoned one longstanding feature that made the ThinkPad P series stand out from the competition — the use of a magnesium subframe, also dubbed the “roll cage,” to add strength and rigidity to the laptop model. Notebookcheck spotted the change, which marks the end of an era that began with the ThinkPad T60 in 2006, the company’s first ThinkPad model after taking over from IBM in 2005. Magnesium alloy is widely used in premium laptop models because of its relative lightness and comparable rigidity, but it’s often used as a material for the external chassis. The ThinkPad P series was a different beast, though. Lenovo built this line of laptops as mobile workstations and ensured that it had the rigidity to face the physically most challenging of situations.…