The EliteBook 745 G2 has an SSD storage medium which is better than most laptops that have been on the market for a comparable time to it. Most portable PCs of this type 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 across all laptops of a comparable age and spec to the EliteBook 745 G2.
Across similar types of laptop the worst storage medium is HDD.