The ZBook 15 has a better storage medium than most portable PCs of this age and type. This HP portable PC has an SSD storage medium, whereas most many processor core portable PCs that have been on the market for 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.
This notebook PC's storage medium (SSD) is in fact the best storage medium amongst all notebook PCs of this spec and age.
Amongst comparable types of notebook PC the worst storage medium is HDD.