The easiest solution is to create recovery media using the built-in recovery media creation tool. Type
recovery media into the start menu and you will get an option for
Recovery Media Creation. Run this program. It will give you the option to create recovery media using blank DVDs or a USB flash drive. In your case, since the dm1 has no DVD drive, you will want to use a flash drive. Unfortunately, this can only be done once per computer, so make sure that you do it right and don't lose the flash drive.
If the need to reinstall your computer with the default image arises, you will boot off of the USB flash drive and be guided through the reimaging process. Your computer will then be exactly how it was when you first received it.
You may also be interested in using the built-in Windows Backup to run regular backups. These backups create full disk images, and can be used to restore your computer to the exact state it was in when the backup was made, even if you have to restore to a completely new disk.
In case you ever want to do a clean re-install, you should also back up the
C:\swsetup folder. This is where all of the drivers for your computer are stored. Many of them are available online, but a few may be difficult to find, such as the WLAN driver on some Pavillion models.