Those who have an Apple TV can use AirPlay to use their TV as a second screen.
Simultaneously supports full native resolution on the built-in display at millions of colors and: 13.3-inch (diagonal) LED-backlit display with IPS technology 2560-by-1600 native resolution at 227 pixels per inch with support for millions of colors.Under Display and Video Support, you will see some details similar to the following : Display You will then be directed to an Apple web page indicating your device’s technical specifications.
Then click Support > Specifications (under Mac Resources).