RDS Virtual Desktop - Unmanaged Collection

I tried to create unmanaged collection with user profile disk - as instructed in support documents.

I prepared several VM but only 2 appears in the selection list - a Win 7 and Win2012 - some other Win7/Win8 which had been sysprep were not listed -- so first question: what is the requirement of target VM/OS?

I created the collection successfully with the VM - Win7 but cannot connect

I then added Win2012 to the collection and the connection succeed with the VM (user data created on user disk)

So here comes question II: what is the requirement of target VM/OS of this kind of collection -- is this only working with Windows server edition?

Thanks,

Leon Li