Apple unveiled fourth-generation 15-inch MacBook Pro models during a press event at their headquarters on October 27, 2016. Introducing the Touch Bar, a multi-touch enabled OLED strip built into the top of the keyboard in place of the function keys. The Touch Bar models also include a sapphire-glass covered Touch ID sensor at the right end of the Touch Bar which doubles as a power button. The models also introduce a "second-generation" butterfly mechanism keyboard that provided more travel than the first iteration implemented on the Retina MacBook. The 15-inch model has a trackpad twice as large as the prior generation.