The Sun Server X2-4 supports dual-rank 4-GB and 8-GB RDIMMs and quad-rank 16-GB RDIMMs. A two-processor system using four riser modules populated with 16-GB RDIMMs supports a maximum of 512 GB of system memory. A four-processor system using eight riser modules populated with 16-GB RDIMMs supports a maximum of 1 TB of system memory.
Dual-rank DIMMs (marked 2Rx4) do not include heat spreaders.
Quad-rank DIMMs (marked 4Rx4) include heat spreaders. DIMMs with heat spreaders have two U-shaped metal clips on the top of the DIMM.