The Mac Pro Late 2013 has an SSD storage medium which is faster than most medium processor core PCs that were released more than a year ago. Most personal computers of a similar age and type 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 personal computer's storage speed (SSD) is in fact the best storage speed amongst all comparable spec computers that are a similar age to the Mac Pro Late 2013.
The worst storage speed amongst comparable types of personal computer is HDD.