A virtual machine (VM) is a software container (sometimes called a "guest") that runs on a host physical computer and that behaves as if it were a physical computer itself. VMs consist of an operating system plus CPU, memory (RAM) and networking resources, and software applications.
A template is a virtual machine encapsulated into a file, making it possible to rapidly deploy new VMs. Each template contains installation metadata—the setup information needed to create a new VM with a specific guest operating system, and with the optimum storage, CPU, memory and virtual network configuration.
You can create new VMs in XenCenter in a number of different ways:
VMs in a XenServer environment may be fully virtualized (HVM) or paravirtualized:
Paravirtualized (PV) drivers are available for Windows and Linux VMs to enhance disk and network performance. These drivers are supplied in the XenServer Tools package and should be installed on all new VMs - see Installing XenServer Tools. XenServer features such as VM migration and historical performance data tracking are only available on VMs that have XenServer Tools installed.
A number of different templates are supplied with XenServer, and these contain all the various configuration settings needed to install a specific guest operating system on a new VM. You can also create your own customized templates configured with the appropriate guest operating system, memory, CPU, storage and network settings, and use them to create new VMs. See the XenServer Virtual Machine User's Guide for a list of the templates/operating systems supported at this release, and for detailed information about the different install mechanisms on Windows and Linux.
You can view the XenServer templates supplied with the product and any custom templates that you create in the Resources pane.
In Server View, you can control whether or not XenServer and Custom templates are shown in the Resources pane: