The second-generation Mac Pro has a redesigned configuration of ports. It has a HDMI 1.4 port, dual Gigabit Ethernet ports, six Thunderbolt 2 ports, four USB 3 ports, and combined digital Mini-TOSlink optical / analog 3.5 mm stereo mini jack for audio output. It also has a headphones mini jack (the two are distinctly selectable within the Sound System Preference panel, Output tab). There is no dedicated port for inputting audio. The system has a low-fidelity internal mono speaker. The Thunderbolt 2 ports support up to thirty-six Thunderbolt devices (six per port) and can concurrently support up to three 4K displays. This design requires two GPUs to support the seven display outputs (HDMI and six Thunderbolt). The I/O panel illuminates itself when the unit senses it has been moved to make it easier for the user to see the ports. Unlike the previous model, it has no FireWire 800 ports, dedicated digital audio in/out ports, a SuperDrive, DVI port, 3.5-inch drive bays for replaceable storage drives, or changeable internal PCIe slots. Instead, there are six Thunderbolt 2 ports to connect high-speed external peripherals, including enclosures for internal PCIe cards.