Installing and Upgrading Ram on a mid 2011 iMac (different size RAM) Apologies for my ignorance here, as the title suggests I am looking for advice on  upgrading the Ram on my mid 2011 iMac. I have bought 2x4GB and the iMac already has 2x2GB. I found the question was already asked by Mike Kwan here: 
How should different sized RAM be added to iMac?

However as I do not have 50 rep, I can not comment and when I went to put an answer in I am told not to ask questions or look for help in the answer.

(So again sorry about the duplication question)

According to Josh " as long as your top two slots are filled using the original factory RAM and you installed the new RAM into the bottom slots" the configuration is good.
So I looked at the image that Mike provided and compared it to the info from my iMac (after I had installed the extra RAM). As the 1st image of my configuration shows Bank 0 and 1/DIMM0 on my iMac contain the 4GB sticks which is in contrast to Mike's picture. I followed the install guide that Josh suggested regarding the "Top and Bottom" slots here: http://support.apple.com/kb/ht1423

Have I missed something or have I done this correct?
My understanding is that you want to pair your memory sticks in order to avail of dual-channelling, and are uncertain if this configuration is compliant.

It is. Firstly, apple recommends keeping the factory memory in the same position as it always has been. Failing that, it's only important to keep the same-sized memory in the same DIMM slot.

As you have above, both 4GB sticks are in the zeroth position, and both 2GB sticks are in the first position. This (or the opposite 2GB in zeroth, and 4GB in first) is the optimal configuration.