The HP Z840 has an HDD storage medium which is faster than the Flash storage medium found on most similar spec personal computers that were launched more than two years ago. A Hard Disk Drive (HDD) is the traditional storage method for computers. A HDD stores the information on magnetic disks. HDD drives are cheap, but they are slower than Flash and SSD bases storage systems.
There are a number of alternative HDD desktop computers currently available that you might also want to look at including cheaper personal computers such as the P900[pl_2535695_price], or the P900[pl_2535706_price] both from Lenovo or the HP Z420[plb_2498184_price].
If the storage speed of this computer is not fast enough for you then you might also want to look at the HP Z440[plb_2466558_price] (SSD) which is also cheaper.