The HP Z420 has a faster storage speed than most medium processor core personal computers that came out more than two years ago. This computer has an SSD storage medium, whereas most PCs that have been on the market for a similar time to it have an HDD storage medium. 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 in fact the best storage speed across all medium processor core personal computers that were launched around the same time as the Z420.
Across similar types of desktop computer the worst storage speed is HDD.