The Sun Server X2–8 now supports dual-rank and quad-rank 16 GB DIMMs. However, mixing dual-rank DIMMs with quad-rank DIMMs in the same CMOD degrades performance.
Dual-rank DIMMs (marked 2Rx4) do not include heat spreaders.
Quad-rank DIMMs are marked 4Rx4 and include heat spreaders. DIMMs with heat spreaders have two U-shaped metal clips on the top of the DIMM.
The following figure shows a DIMM with heat spreaders.