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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. 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. 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.