The Lenovo W540 has an SSD storage medium which is better than most portable PCs of a similar age and spec to it. Most laptops that are a similar age 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.
This portable PC's storage medium (SSD) is in fact the best storage medium amongst all laptops of a similar spec and age to the W540.
An HDD storage medium is the worst storage medium across similar types of portable PC.