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Server hardware- ram data width 4x vs 8x(is there a significant differ

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December 7, 2012 5:07:25 PM

So I'm figuring out hardware for a new virtual host and I noticed that in all the dell servers now I can pick 4x or 8x data width memory.

Another place I find this popping up is when shopping ram on crucial. Crucial labels it as "x4 based" or "x8 based"
in their module details.

DDR3 PC3-10600 • CL=9 • Quad Ranked • x4 based • Load Reduced • ECC • DDR3-1333 • 1.35V • 4096Meg x 72 • • Part #: CT2948062

I couldn't find any reviews or articles benchmarking what the difference was. Does anyone have a good explanation of real world performance differences? How about mixing 4x dimms with 8x dimms in a server?
a b } Memory
December 7, 2012 5:27:56 PM

Most DIMMs are built using "×4" (by 4) memory chips or "×8" (by 8) memory chips with 9 chips per side. "×4" or "×8" refer to the data width of the DRAM chips in bits.
In the case of the "×4"-registered DIMMs, the data width per side is 36 bits; therefore, the memory controller (which requires 72 bits) needs to address both sides at the same time to read or write the data it needs. In this case, the two-sided module is single-ranked.
For "×8"-registered DIMMs, each side is 72 bits wide, so the memory controller only addresses one side at a time (the two-sided module is dual-ranked).

Sometimes memory modules are designed with two or more independent sets of DRAM chips connected to the same address and data buses; each such set is called a rank. Since all ranks share the same buses, only one rank may be accessed at any given time; it is specified by activating the corresponding rank's chip select (CS) signal. All other ranks are deactivated for the duration of the operation by having their corresponding CS signals deactivated. DIMMs are currently being commonly manufactured with up to four ranks per module. Consumer DIMM vendors have recently begun to distinguish between single and dual ranked DIMMs.
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