The Inspiron 15 7558 has an HDD storage medium which is better than the SSD storage medium found on most 2 in 1 laptops that came out more than a year ago. HDD is a traditional storage drive which stores the information on magnetic disks. HDD drives are slower than other forms of storage such as solid state drives (SSD) and flash drives.
This notebook PC's storage medium (HDD) is in fact the worst storage medium across all 2 in 1 laptops that have been on the market for more than a year.
Across comparable types of notebook PC the best storage medium is SSD.
If you want a laptop with a better storage medium then you might want to consider the HP 13-r100dx ($850.46) (Hybrid-HDD).