In a Citrix XenApp environment, the hardware layer is the sphere that contains a hypervisor and its underlying physical hardware. The hardware layer participates in the XenApp infrastructure by running the OS resources and keeping VM workloads highly available.
Since we've mostly focused on building a virtualized environment in this book, the entire Citrix infrastructure will reside on virtual machines running on a hypervisor. In this deployment, the XenServer hypervisor (version 6.2 SP1) will be used, but you can leverage your existing host infrastructure to build a XenApp solution as long as it is supported by Citrix. The following host platforms are currently supported for XenApp 7.6: