The HP Stream 11-d070nd has a better storage medium than most laptops that have been on the market for around the same time as it. This HP portable PC has an SSD storage media, whereas most laptops that have been around for around the same time as it have an HDD storage media. 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 laptop's storage medium (SSD) is in fact the best storage medium across all laptops of this age and spec.
The worst storage medium amongst comparable types of laptop is HDD.