All PowerEdge 840 system boards (motherboards) support either PC2-4200E (533MHz) or PC2-5300E (667MHz) DDR2 ECC-registered memory DIMMS when installed in matching pairs. System boards will support up to 8GB RAM with the most current BIOS revision. RAM must be installed in pairs of matching size, rank and technology.
Dell part numbers for memory normally signify individual DIMMs, whereas third-party memory like Kingston sometimes come in kits of two DIMMS.
If you need assistance with installing memory modules, download the Dell PowerEdge 840 owner's manual and look for the System Memory section under Installing System Components.
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