The Stream 13 has an SSD storage medium which is better than most notebook PCs of a similar type and age to it. Most portable PCs of a similar age and type to it have an HDD storage medium. 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.
This notebook PC's storage medium (SSD) is actually the best storage medium amongst all laptops that have been on the market for more than a year.
The worst storage medium across similar types of notebook PC is HDD.