The T5500 Memory config manual shows options for populating the DIMM slots.  There is a column called DIMM Rank.  I believe SR is single rank, DR is dual Rank, but what is MR? (Mixed, quad?)

The other question I have is for a 24GB option using 4GB DIMMs, it has a DR in the rank column.  Does this mean only Dual Rank 4GB moudles can be used, or will Single Rank 4GB modules work?

Thanks!