The EliteBook 820 has an SSD storage medium which is better than the HDD storage medium found on most notebook PCs of this age and spec. 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 portable PC's storage medium (SSD) is in fact the best storage medium across all laptops of a comparable age and type to the EliteBook 820.
An HDD storage medium is the worst storage medium amongst comparable types of portable PC.
It may also be worth considering one of the other notebook PCs that have an SSD storage media currently available including the X1 Carbon, or the X1 Carbon both from Lenovo or the HP EliteBook 850 (£1,198.78) which is cheaper.
Portable PCs with a better storage medium that might also be worth looking at include the Lenovo T420s (£972.00) (SSD), or the Toshiba Tecra Z50 (£1,503.59) (SSD).