The Stream 11 has an SSD storage medium which is better than the HDD storage medium found on most notebook PCs of a comparable age and spec to it. Flash drives store data in semiconductors on a circuit board rather than using magnetic or optical media. Flash have no moving parts which makes them very fast and reliable.
An SSD storage medium is actually the best storage medium across all laptops of this type and age.
An HDD storage medium is the worst storage medium across similar types of laptop.