The ProBook 655 G1 has an SSD storage medium which is better than most many processor core laptops that have been available for around the same time as it. Most many processor core laptops that were released more than two years ago 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 many processor core laptops that were released around the same time as the ProBook 655 G1.
The worst storage medium amongst similar types of laptop is HDD.