It's because the resolution (number of pixels wide x number of pixels high) has been set for a standard screen rather than a wide screen.
Look up the resolution of the physical screen and set the display properties resolution to the same.
Alienware 17 R4 2017 review
Interview: Camille Walala on her giant 3D installation inspired by childhood funfair visits
Best iPad buying guide 2017
Où regarder le British Open 2017 ?