‘Silent’ is a word that is greatly over used in the PC industry. Power supplies, CPU coolers and video cards are all marketed as being silent, despite featuring fans or other moving parts. These products may well be quiet, but they are definitely not silent.
Chillblast’s Fusion Vacuum PC is different. It is 100% passively cooled in nature, has no moving parts whatsoever outside of the optical drive, and the manufacturer claims that it makes no sound whatsoever.