The Lenovo W540 has an SSD storage medium which is better than the HDD storage medium found on most laptops of a similar spec and age to it. 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 across all portable PCs that have been available for around the same time as the W540.
An HDD storage medium is the worst storage medium across similar types of portable PC.