The Apple Mac Mini Late 2014 has an SSD storage medium which is faster than most few processor core PCs that have been on the market for around the same time as it. Most computers that are a comparable age 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 desktop computers of a similar age and spec to the Mac Mini Late 2014.
The worst storage speed amongst similar types of desktop computer is HDD.