Single Ranked versus Dual Ranked Memory DIMMS

Question

Can anyone expain the difference between single ranked and dual ranked memory DIMMs?   I can't find any info on this subject.  There is one old posting with this question from December with no responses.    I just trying to spec out a new PowerEdge 2850.   Any comments on perfromance expectations or differences would be greatly appreciated.   Thanks, Roger

speedstep · Answer

Systems like the Precision 470 have 6 slots.

However not all the slots support the Dual Ranked memory.

Dual Ranked parts (currently 2GB memory Module) are used in banks 3 and 4

Memory Details for Dell Precision Workstation 470, 470n
Standard Memory : 512MB (Removable)
Maximum Memory : 16GB

Total Memory Slots : 6 (3 banks of 2)
Memory Type : DDR2 PC2-4200 (533MHz) ECC DIMM
Notes : INSTALL IN PAIRS FOR DUAL CHANNEL MODE. When Dual Ranked parts (currently 2GB memory Module) are used in banks 3 and 4, then banks 5 and 6 must be left empty

That means to get 16 gigs you must use 4 pc of dual ranked Memory at 4 gigs each When they become available.

http://www.kingston.com/ukroot/serverzone/technicalbrief/Mem_ranks_ENG.pdf

General Memory Module Installation Guidelines
If only one memory module is installed, it must be installed in socket DIMM1_A.

If two or more memory modules are installed, they must be installed in pairs of matched memory size, speed, and technology.

The system supports both single-ranked and dual-ranked memory modules.

If you install both single-ranked and dual-ranked memory modules, the dual-ranked memory modules must be installed in bank 1.

Dual-ranked memory modules are not supported in bank 3.

If dual-ranked memory modules are installed in bank 2, you cannot install memory modules in bank 3.

Austin_Bike · Answer

Ranks are, simplistically, addressable memory locations.   To get the best performance, you want to maximize the total number of ranks.  For instance  4 1GB single rank DIMMs (4 total ranks) will give you better performance than 2 2GB single rank DIMMs (2 total ranks). The chipset will support up to 8 total ranks   Think of it like spindles in RAID.   However, dual ranked DIMMs are less expensive, so your choice is either best performance (maximize ranks) or lowest price (choose larger dual ranked pairs.)   For the majority of applications you probably won't see a difference, but on real processor/memory intensive applicaitons like technical computing and HPCC you may see a difference, but in I/O heavy applicaitons like messaging and database you'll see less impact and should focus on best price.

PowerEdge Hardware General

Single Ranked versus Dual Ranked Memory DIMMS

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