The EliteBook 755 G2 has an SSD storage medium which is better than most laptops that were released around the same time as it. Most portable PCs of this spec and age 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 notebook PCs of a comparable type and age to the EliteBook 755 G2.
An HDD storage medium is the worst storage medium across similar types of laptop.
There are a number of other notebook PCs that have an SSD storage media currently available that you might want to look at including the Asus U500VZ which has better reviews.