Proper Windows 8-64 bit driver for Arduino Yún (Yun)
What is the chipset that is used [in the] [Yún] board for USB communication [...] ?


The Arduino Yún has two USB interfaces:


A USB interface built in to the ATmega32U4-AU which manages serial comms.
A USB 2.0 hub based on an AU6350


See schematic


  The ATmega32U4 provides a dedicated UART TTL (5V) serial communication. The 32U4 also allows for serial (CDC) communication over USB and appears as a virtual com port to software on the computer. The chip also acts as a full speed USB 2.0 device, using standard USB COM drivers.


...


  The Yún appears as a generic keyboard and mouse, and can be programmed to control these input devices using the Keyboard and Mouse classes.


See Arduino Yún