The ProDesk 400 G1 has an SSD storage medium which is faster than the HDD storage medium found on most medium processor core PCs that are a similar 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 across all medium processor core PCs that are a comparable age to the ProDesk 400 G1.
An HDD storage medium is the worst storage speed amongst comparable types of personal computer.