The thickness of all laptops is measured with the screen fully closed.
Shared video RAM uses part of the system RAM for video processing; the graphics capability on Recommended Models are more than sufficient for engineering use, and it uses less power than other methods. Does not possess as much processing capability as a Discrete video RAM.
Discrete video RAM uses its own dedicated RAM for video processing; the graphics capability is greatly enhanced compared to a laptop with shared video RAM, but it also results in increased power consumption.
Switchable video RAM means that the computer can use either of the above methods; you can choose which you'd like to use for a given situation, which is why these laptops have two video cards listed.