The NP915S3G has a better storage medium than most notebook PCs of a comparable age and spec to it. This portable PC has an SSD storage medium, whereas most portable PCs that have been on the market for a comparable time to it have an HDD storage medium. 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 actually the best storage medium across all portable PCs of this age and type.
The worst storage medium across similar types of portable PC is HDD.