The HP Z420 has an HDD storage medium which is faster than the Flash storage medium found on most many processor core 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 PCs currently available that you might also want to look at including the HP Z640[plb_2520401_price] which is cheaper.
If you want a computer with a faster storage speed then you might also want to consider the HP Z440[plb_2466558_price] (SSD), or the Lenovo Thinkstation P500[plb_2535509_price] (SSD) which is also cheaper.