The EliteBook 840 has an SSD storage medium which is better than most medium processor core laptops that have been around for around the same time as it. Most laptops that have been around for 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.
An SSD storage medium is actually the best storage medium across all similar spec notebook PCs that have been available for a comparable time to the EliteBook 840.
An HDD storage medium is the worst storage medium across similar types of portable PC.
Other laptops that have an SSD storage media currently available which you might also want to consider include cheaper notebook PCs such as the Toshiba Tecra Z40.
If you would prefer a portable PC with a better storage medium then you might want to consider the Asus Zenbook UX305 (ssd and cheaper).