The CPU would be passively cooled by simply having a heatsink with no fan attached to it. It relies on the airflow of other fans, or natural airflow if there aren't any, to remain cool.
A fan could be almost right next to it, but not attached, and it'd still technically
be passively cooled. Unless the cooling on the CPU itself is active, then it's passive (relying on something other than the attached cooling).
There's also the scenario where there's some sort of duct or shroud (ala, a Dell) making a fan (such as an exhaust fan) almost double as the CPU fan. Even in this case, the CPU is still
technically passively cooled. The fan is acting to cool the CPU, true, but it's still acting first and foremost as the exhaust, and the duct/shroud merely forces air being exhausted over the CPU heatsink first. That is the very definition of passive, something with no attached fan that relies on something else.
So, in short, to be passive means it has no fan on the heatink. That's all there is to it. Any other fans cooling it, lined up with it, etc., it's still passive.
Originally Posted by Machiyariko
The reason why I'm asking is that my current setup has option 2 and I'm wondering if you can really call that passively cooled.
If that's the case, "technically", yes, it is passively cooled, but since it may be up to interpretation, it depends. In definition, though, yes, I'd say you are passively cooled. The heatsink has no fan, and you're not just cheating by heaving it literally right on it without being attached.Edited by Princess Garnet - 5/2/11 at 10:38pm