For prebuilds the tech support will often provide a link for downloading the iso images for creating a disk set where files are spread over more then one disk once you provide the needed customer account and serial number information. That allows restoration of the original preinstall of Windows there.
When a new system is bought without seeing the recovery disks included that is one way to see a system restored to factory condition. On the latest Dells apparently you simply press a key combo to see the primary reformatted and Windows reinstalled to factory without the need for disks. You simply follow the instructions in the user manual for restoration there.