[CentOS] Checking fan state

Christopher Chan wrote:
>> It is a 4-pin connector, and I think there is a guide, or one side is
>> different than the other. That is why I think I could not have but in in 
>> backwards.
>>     
>
> Okay, not the stuff you get on boards that are not 'branded'.
>   

MANY newer desktop CPU fans are 4 pin...  this way there is power, tach 
output and PWM control on separate pins (and ground)....     doing PWM 
speed modulation on a 3 pin fan makes reading the tach kind of hard.

but, as you noticed, we are dealing with a HP NC2400 laptop here.
http://h10010.www1.hp.com/wwpc/us/en/sm/WF06a/321957-321957-64295-321838-306995-1847110.html