Q I have upgraded the memory in my 2010 27” iMac from 4 to 12 GB. I did this by installing additional memory modules in the two spare slots. The correct total is now reported in its system information. Should I have switched the old and new memory in order to obtain maximum benefit?

A Some models, such as high-performance Mac Pros and older desktops, are sensitive to the disposition of memory modules, as they use design tricks such as ‘interlacing’ to optimise performance.

This is not the case with your iMac, and there is nothing to be gained by rearranging the memory installed in it. Apple does impose limits on installing single modules, with details for recent iMac models given here.

Updated from the original, which was first published in MacUser volume 28 issue 08, 2012.