I was somehow able to reach the "Live chat" type helper at dell regarding upgrading my computer memory to 16 gb of memory. I have a Studio XPS 9100 with 8gb of existing memory. They are in the form of four 2gb chips in slots 1, 2 ,3 (blue) and 4 (pink). I was told by the expert helper that since I had two empty slots ( 5 and 6 - pink) that is where I should put my two additional 4gb chips to get to 16gb. I did that and I am now showing I have a total of 12gb, not 16. Windows 7 Pro is supposed to support up to 16gb. (The XPS 9100 will run up to 24gb but I am not trying to go there.)

I know little about comuters but I am receiving the impression that slots (DIMM connectors) 4, 5 and 6 (pink) match and should be loaded first and slots 1, 2 and 3 (blue) match and should be loaded last.

Since I have 2 gb in slots 1, 2, 3 and 4 that means the first/controlling slots 4 & 5 match(?). The follow-up slots 1 and 2 match with 2gb each. However slot 6 with 4gb does not match with slot 3 with 2gb and that is why I am only seeing 12gb as available memory in my computer properties? 

Did Dell steer me wrong?

Is there a fix

what should I have done

sooo many questions