The HP Z420 has an SSD storage medium which is faster than the HDD storage medium found on most medium processor core personal computers that are a comparable age to it. Solid State Drives (SSD) store information in transistors on a circuit board rather than on optical or magnetic media. This has the advantage of being much faster than a traditional HDD drive.
An SSD storage medium is actually the best storage speed amongst all desktop computers of a comparable spec and age to the Z420.
An HDD storage medium is the worst storage speed amongst similar types of computer.
Alternative SSD personal computers currently available which you might want to consider include because of it's better review score, the DELL Precision T1700 SFF[plb_2676603_price].