From Red Hat Software:
A base Red Hat Enterprise Linux server provides fully-virtualized guest support for Red Hat Enterprise Linux 3, 4, and 5. Third party operating systems may also be hosted. Fully-virtualized guest support requires hardware features provided by Intel Virtualization Technology and AMD-V processors. Para-virtualized guests can be configured on any 32-bit x86 (with PAE support), 64-bit x86, or Itanium2 system. With Red Hat Enterprise Linux Advanced Platform the number of guest operating systems that may be hosted is unlimited, constrained only by physical hardware resources.
What's new in this version:
Version 6.4 has improved Virtual Guest Experience on VMware and Microsoft Hyper-V and updated Resource Management Capabilities.