The models introduced the Touch Bar, a multi-touch enabled OLED strip built into the top of the keyboard in place of the function keys. They 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. All ports have been replaced with either two or four combination USB-C 3.1 ports that support Thunderbolt 3 and dual DisplayPort 1.2 signals, any of which can be used for charging. The MacBook Pro is incompatible with some older Thunderbolt 3 certified peripherals, including Intel's own reference design for Thunderbolt 3 devices. Furthermore, MacOS on MacBook Pro blocks certain classes of Thunderbolt 3 compatible devices from working by blacklisting them. Devices using HDMI, previous generation Thunderbolt, and USB will require an adapter to connect to the MacBook Pro. The models come with a 3.5 mm headphone jack, although TOSLINK functionality of older generation MacBook Pros has been removed.