I am personally using the following:
1. A Dell PowerEdge T20 Server, Intel Xeon E31225v3 3.2GHz 4C (Quad Core with 32GB RAM).
2. Windows Server 2012 R2 with Hyper-V (as the parent system).
3. Multiple (child) VMS running Server 2012 R2 and serving as Domain Controllers, SQL 2012, Exchange 2013 and SharePoint 2013.