Asus VivoTab RT - Manual (Page 13)

TF600T 1
Windows® 8 touch button
Touch this button to go back to the Start screen. If you are already in the
Start screen, touch this button to go back to the last app you opened.
Dock port
Use the dock port to charge the battery pack or supply power to your
Tablet PC. This port also allows you to connect the bundled USB dongle
for USB 2.0 connectivity.
If you purchased an optional mobile dock, you can connect it to the dock
port to support keyboard, touchpad, and USB 2.0 port functions.