What is a "Silent" Computer?

@ 2006/09/22
Admittedly, it's a bit odd that Silent PC Review has taken over four years to publish an article that deals explicitly with what a "silent" computer is, exactly. This seemingly innocuous question is far from simple. Trying to answer it gets at the heart of PC acoustics issues, and the challenges for those trying to create or document a "silent" computer.
Comment from wutske @ 2006/09/24
a real silent computer is a computer of wich I can not say wheter it's on or off just by listening to it (in normal ambiant sound).
a normal silent computer is a computer I won't notice/get annoyed by when I'm working on it, another important thing is that it lacks low (big fan) or high (hdd) frequency sounds.
Comment from Kougar @ 2006/09/24
Nah, it's an easy question!

Any computer I can sleep 4 feet away from and not think twice about the noise would fall under "silent" in my book.
Comment from Rutar @ 2006/09/22
but not a word on sone in the end :/