The Shuttle XS 3500BB V4 has an SSD storage medium which is faster than the HDD storage medium found on most medium processor core personal computers that have been on the market for a similar time to 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 actually the best storage speed amongst all PCs of a similar age and spec to the XS 3500BB V4.
The worst storage speed amongst similar types of PC is HDD.