The Mac Pro Late 2013 has an SSD storage medium which is faster than most comparable spec desktop computers that are a similar age to it. Most personal computers that have been available 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.
This computer's storage speed (SSD) is in fact the best storage speed amongst all medium processor core computers that have been on the market for more than a year.
The worst storage speed amongst comparable types of computer is HDD.