The DELL XPS 13 has an SSD storage medium which is better than most laptops of a similar age and spec to it. Most laptops that have been around for a comparable time to it have an HDD storage medium. Solid State Drives (SSD) store data in semiconductors on a circuit board rather than using magnetic or optical media. Solid State Drives have no moving parts which makes them very fast and reliable.
This portable PC's storage medium (SSD) is in fact the best storage medium amongst all notebook PCs of a comparable spec and age to the XPS 13.
An HDD storage medium is the worst storage medium amongst similar types of portable PC.
Notebook PCs with a better storage medium that might also be worth looking at include the DELL XPS 13 (SSD).