What limits a motherboard from supporting more memory?
I have noticed, that 8Gb RAM modules finally appeared in the desktop market. Also most of the new motherboards specs state that the maximum of 32Gb is supported and so 8Gb modules too. However, even 1-year old motherboard had only 4Gb modules specified in the manual.
So my question is: does the upper limit for module size exists? (e.g. does old MBs support 8GB modules, whenonly one such module is used, so the max memory constraint isn't violated) If it is, what's the reason for it, especcially, when both MBs use the same north/south bridge?
P.S. Modified version of a previous question. I just wanted to edit it, but it was closed ((( Hopefully this one won't be, cause I haven't find question about modules only.