Cant type hangul yet T.T
https://wiki.archlinux.org/index.php/NVIDIA_Optimus
If you are installing Arch on USB, you might run into trouble: When you logon the screen "freezes" but the system itself seems to be fine, if you use Alt+Ctrl+F4 or what ever to move to another console. It is the graphics environment that isn't displaying correctly. In addition to that, you can confirm that by typing "ps" command and see things are in fact, running.
If you are in this situation, follow the instructions in NVIDIA_Optimus.