The Stream 13 has an SSD storage medium which is better than most notebook PCs of a comparable spec and age to it. Most notebook PCs that were released more than two years ago 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.
An SSD storage medium is in fact the best storage medium across all comparable spec portable PCs that have been around for more than two years.
An HDD storage medium is the worst storage medium across similar types of laptop.