The Stream 11 Pro has an SSD storage medium which is better than the HDD storage medium found on most laptops of a similar age and spec to it. 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 in fact the best storage medium across all laptops of a similar spec and age to the Stream 11 Pro.
The worst storage medium across comparable types of notebook PC is HDD.