The Lenovo T440 has an SSD storage medium which is better than most portable PCs of this spec and age. Most medium processor core laptops that came out around the same time as 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 amongst all similar spec notebook PCs that have been on the market for a comparable time to the T440.
The worst storage medium across similar types of portable PC is HDD.