Operating system of the template VM. For Linux, the clone is configured at boot through Proxmox's cloud-init parameters (username, SSH key, IP, DNS) and Java can be auto-installed. For Microsoft Windows, the clone boots from a sysprep-generalised image with OpenSSH and Java preinstalled; the cloud-init and Java install fields are hidden because they have no effect on Windows VMs, and Remote FS Root must be set explicitly.