Im not entirely knowledgeable on this, but from my understanding of memory so far in life, is single rank memory is single sided memory (eg memory chips on one side) and dual rank memory is memory chips located on both sides of the chip.
And yes, you would fill up the motherboards ranks faster with double rank ram becuase dual rank ram has a higher capacity than single rank
say you have 8 ranks on your board and 8 ram slots.
You would only be able to load 8 * 1 rank cards, however, you would only be allowed to allocate 4 slots with dual rank memory (4 * 2 = 8)
Hope this helps, I have never run into a rank alocation problem, also, i dont know where to look either to find the rank limitations for a desktop motherboard unless your running a mac
BTW dual rank ram is MORE dense than single rank ram. It is more dence because you have ram chips populating both sides of the ram card versus one with single rank.
EG: you buy two chips of samsung ram. They both are (in theory) the highest capacity ram on the market (this is just a theory, learning only) one chip of ram is single rank with 4 ram chips on one side, the other is dual rank with 4 ram chips on each side (8 total). each ram chip on each card is 512 mb. therefore the single rank card would have a max capacity of 2gb while the dual rank would have a max capacity of 4gb.
