The Flex 15D has an HDD storage media which is better than most 2 in 1 laptops that have been on the market for around the same time as it. Most laptops of a comparable type and age to it have an SSD storage media. 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.
An HDD storage media is actually the worst storage medium amongst all similar spec laptops that have been available for more than two years.
An SSD storage media is the best storage medium amongst similar types of notebook PC.