The Lenovo Flex 15D has an HDD storage medium which is better than the SSD storage medium found on most 2 in 1 laptops that have been around for a similar time to it. 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 portable PC's storage medium (HDD) is in fact the worst storage medium across all similar spec portable PCs that were released around the same time as the Flex 15D.
Across comparable types of portable PC the best storage medium is SSD.