If you install Windows 2008R2/2008/7/Vista as virtual machine in Hyper-V 2012 R2, and notice unknown devices show in device manager.
Actually one is Automatic Virtual Machine Activation (AVMA), and another one is Remote Desktop Control Channel/Enhance Session Mode. This two features are new in Windows Server 2012 R2, and required virtual hardware.
1. You can find the driver in Hyper-V 2012 R2 integration service setup disc or download the driver from link below:
2. Update the driver manually in device manager.
3. Restart Computer.