The HP Pro has an SSD storage media which is better than most similar spec notebook PCs that have been available for around the same time as it. Most similar spec notebook PCs that are a comparable age to it have an HDD storage media. 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 notebook PC's storage medium (SSD) is actually the best storage medium amongst all notebook PCs that are a comparable age to the Pro.
The worst storage medium across comparable types of notebook PC is HDD.