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Every VM is created from a base image, which is a template or ISO which has been created and stored in &PRODUCT;. Both cloud administrators and end users can create and modify templates, ISOs, and VMs. In &PRODUCT;, you can change an existing VM's base image from one template to another, or from one ISO to another. (You can not change from an ISO to a template, or from a template to an ISO). For example, suppose there is a template based on a particular operating system, and the OS vendor releases a software patch. The administrator or user naturally wants to apply the patch and then make sure existing VMs start using it. Whether a software update is involved or not, it's also possible to simply switch a VM from its current template to any other desired template. To change a VM's base image, call the restoreVirtualMachine API command and pass in the virtual machine ID and a new template ID. The template ID parameter may refer to either a template or an ISO, depending on which type of base image the VM was already using (it must match the previous type of image). When this call occurs, the VM's root disk is first destroyed, then a new root disk is created from the source designated in the template ID parameter. The new root disk is attached to the VM, and now the VM is based on the new template. You can also omit the template ID parameter from the restoreVirtualMachine call. In this case, the VM's root disk is destroyed and recreated, but from the same template or ISO that was already in use by the VM.