The Mac Pro Late 2013 has an SSD storage medium which is faster than the HDD storage medium found on most similar spec desktop computers that were released around the same time as 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 in fact the best storage speed across all personal computers that are a comparable age to the Mac Pro Late 2013.
An HDD storage medium is the worst storage speed across similar types of personal computer.