The ProBook 640 G1 has an SSD storage medium which is better than most notebook PCs of a comparable age and type to it. Most medium processor core notebook PCs that were released 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.
This portable PC's storage medium (SSD) is actually the best storage medium amongst all laptops that were launched around the same time as the ProBook 640 G1.
The worst storage medium across comparable types of portable PC is HDD.
If the storage medium of this portable PC is too bad for you then you might want to look at the T420s (£1,388.87) (SSD), or the S540 (SSD) both from Lenovo.