XenServer Tools provide high performance Windows drivers and a management agent that enhances performance between the XenDesktop. The paravirtualization drivers in XenServer enable Windows running in the user space DomU to access the resources in the hypervisor kernel space, or Dom0.
Initially, Citrix systems produced paravirtualized drivers for Windows as part of their commercial XenServer virtualization suite. Now, these drivers are available as a standard distribution with the XenServer hypervisor, as a result of Citrix recently submitting the XenServer project to the Apache Open Source Foundation. Advanced features of XenServer and XenCenter require purchase of the commercial version from Citrix.
You could conceptually run Windows virtual machines in open source Xen. Before Citrix submitted the XenServer product back into the open source community through the Apache foundation, it lacked PV drivers for Windows, and performance would therefore suffer greatly. Today, the...