The Mac Mini Late 2014 has an SSD storage medium which is faster than the HDD storage medium found on most similar spec computers that were launched more than two years ago. 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 similar spec PCs that are a comparable age to the Mac Mini Late 2014.
Across similar types of PC the worst storage speed is HDD.