The EliteBook 820 has an SSD storage medium which is better than most laptops of this type and age. Most comparable spec portable PCs that were launched around the same time as 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.
An SSD storage medium is in fact the best storage medium amongst all laptops that have been available for a similar time to the EliteBook 820.
An HDD storage medium is the worst storage medium across comparable types of portable PC.
Notebook PCs with a better storage medium that might be worth looking at include the DELL Latitude 12 E7250 (SSD).