The JUA365 USB 3.0 to Dual HDMI Multi-Monitor Adapter acts as an external video card for your Mac or PC. It allows you to add an additional monitor/display through your USB 3.0 port. There's no need to open your computer to add an expensive video card. With the USB 3.0 to Dual HDMI Multi-Monitor Adapter you simply load the drivers, plug the adapter into the USB port, then plug in the HDMI monitor cable into the adapter and you are ready. The Adapter supports three viewing modes. Primary Mode allows you to have individual applications open on each monitor, vastly improving productivity. Extended Mode allows you to extend your desktop across multiple displays, which is great for spreadsheets.