The UX305FA has an SSD storage medium which is better than most similar spec portable PCs that have been on the market for a comparable time to it. Most medium processor core laptops that have been available for a comparable time to 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.
An SSD storage medium is actually the best storage medium across all medium processor core laptops that came out more than a year ago.
An HDD storage medium is the worst storage medium across similar types of laptop.