The ProBook 655 G1 has a better storage medium than most notebook PCs that have been available for a comparable time to it. This laptop has an SSD storage media, whereas most similar spec notebook PCs that were released more than two years ago have an HDD storage media. 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 laptop's storage medium (SSD) is in fact the best storage medium across all laptops of a similar type and age to the ProBook 655 G1.
The worst storage medium amongst similar types of laptop is HDD.