6GB vs 4GB - why 6GB slower bandwidth ?

[eva2000]

Just installed Win 2008 Enterprise 64bit for a run

Strange that 2x2GB (4GB) is slightly faster than 2x2GB + 2x1GB (6GB) even at same timings ??? And since these results also appear in memtest it ain't just a Win2008 issue. Maybe Asus Blitz Formula related ?

Using 2x2GB Gskill PC2-8000CL5D-4GBPQ + 2x1GB Gskill PC2-8500CL5D-2GBPK so both kits are non-Micron D9 based

• 9x333FSB 1:1 333Mhz 2x2GB 5-5-5-15 3-42-6-3-3 memtest bandwidth = 3500+ MB/s and Super Pi 8M = 3m 24s
• 9x333FSB 1:1 333Mhz 2x2GB + 2x1GB 5-5-5-15 3-42-6-3-3 memtest bandwidth = 2025 MB/s and Super Pi 8M = 3min 32s
• 7.5x400FSB 4:5 500Mhz 2x2GB + 2x1GB 5-5-5-15 3-52-6-3-3 memtest bandwidth = 2994MB/s ???
• 7.0x429FSB 4:5 536Mhz 2x2GB + 2x1GB 5-5-5-15 3-52-6-3-3 memtest bandwidth = 3212MB/s ???
• 6.5x462FSB 5:6 554Mhz 2x2GB + 2x1GB 5-5-5-15 5-52-7-5-5 memtest bandwidth = 3186MB/s ???
• 6.5x462FSB 5:6 554Mhz 2x2GB + 2x1GB 5-5-5-15 4-52-7-4-4 memtest bandwidth = 3249MB/s ???
• 6.5x462FSB 5:6 554Mhz 2x2GB + 2x1GB 5-5-5-15 3-52-6-3-3 memtest bandwidth = 3315MB/s ???
• 9.0x445FSB 4:5 556Mhz 2x2GB + 2x1GB 5-5-5-15 3-52-6-3-3 memtest bandwidth = 3329MB/s ???
• 7.5x534FSB 1:1 534Mhz 2x2GB 5-5-3-15 3-52-6-3-3 memtest bandwidth = 5872 MB/s

Any ideas why it 6GB config is clock for clock slower ???

[Omastar]

More stress on the MCH?

[dduckquack]

dual channel problems?

[alexio]

I think it has to do with bank interleaving. In this configuration the memory controller actually handles the memory as 3x2=6 (dual channel) bank whereas in a 2x2GB configuration the memory controller handles the memory as 4x2=8 banks.

*EDIT* Looking at those numbers dual channel isn't really enabled.

[Cronos]

I hope same size modules are installed in the same color slots?

[Spyrus]

Different modules maybe result in single channel mode according to this from
anandtech
http://www.anandtech.com/mb/showdoc.aspx?i=3208&p=3

Additionally, each FSB bus cycle "phase" for each channel can be further manipulated. "CHA" and "CHB" refer to the two independent memory channels in a dual-channel memory configuration. Installing only one memory DIMM, or certain combinations of mismatched memory module pairings across all four expansion slots, results in the motherboard defaulting to single-channel operation; otherwise there are two memory channels in operation, which enhances overall system performance. The number of phases per channel depends on the memory divider in use (each channel will always have the same number of channels though) - a 3:2 memory divider has two phases, 4:3 has three, and 8:5 has five, for example. We will explore the theory behind this truth shortly.

[eva2000]

Yeah looks like dual channel isn't enabled but same sized modules are in same coloured slots. Just tried 4x1GB and it's fine i.e. 556Mhz 5-5-4-15 at 1.92v works fine with 5600+ MB/s memtest bandwidth.

[Kunaak]

odd pairings of ram has always resulted in bad results.
its been this way as long as I could remember.

[STEvil]

number of chips (ranks more technically) on each stick of ram must match for dual channel to enable "correctly"

[Jamestuk]

number of chips on all of the ram sticks, or just same for 1 and 3 (say 8 here) and same for 2 and 4 (say 16 chips here)

[Spyrus]

ranks are not based on number of chips i think.

[eva2000]

Ah ha looked into manual and it's by design that 6GB would have lower bandwidth than 4GB

You may install varying memory sizes in Channel A and Channel B. The system maps the total size of the lower-sized channel for dual channel configuration. Any excess memory from the higher-sized channel is then mapped for single channel operation

[Yoxxy]

Enterprise Server 2007 is quite expensive. Can't believe you would buy that just to run pi...
You have too much money eva...

[eva2000]

Microsoft TechNet Direct subscription

or the 240 day evaluation trial

[Slay0r]

Enterprise Server 2007 is quite expensive. Can't believe you would buy that just to run pi...
You have too much money eva...

pretty sure you mean 2008, eitherway you can download the enterprise 240days trial off microsoft website.

[Yoxxy]

Microsoft TechNet Direct subscription

or the 240 day evaluation trial

Ah did not know there was a trial version.

Seems like a nice OS.