What are these Clusters of Tiny Components on the Underside of my MotherBoard within my PC?!?

I purely took the Panels off of my PC I built final January. I figured I should check for Dust, and verbs it out. I noticed that on the Back (Underside) of my MotherBoard, in that are 3 Clusters of Tiny Components.



I remember seeing them before, I basically never realy thought that much of them. But what made me so Curious, is that I finally noticed that 2 of these Clusters are underneath the North & South Bridges.



Their is a Small Cluster right underneath of the CPU (K8).

I know this before.

Their is a Larger Cluster right underneath of the North Bridge.

Their is also a similar sized Cluster underneath the South Bridge.



Now, this get me Thinking!! Why are they underneath these Key Locations? And what are they for?!? What do they Do?!?

What are these Clusters of Tiny Components on the Underside of my MotherBoard within my PC?!?

Are these really tiny? They are probably surface mount capacitors and possibly also surface mount resistors. The capacitors are probably being used to filter roar and EMI from the DC supply tracks for the chips. Also some devices use external capacitors to generate timing signals.
The MoBo manufacturer have to modify the main board after production to make it work properly.