The Chromebox has an SSD storage medium which is faster than most similar spec computers that came out around the same time as it. Most similar spec computers that have been available for a comparable 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.
An SSD storage medium is actually the best storage speed across all desktop computers that are a similar age to the Chromebox.
Across comparable types of computer the worst storage speed is HDD.