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At work I have a dual CPU workstation (HP Z600) with i7 / Xeon E5620 Gulftowns installed on a Intel 5520 based motherboard. Factory, it was installed with 2x2GB sticks enabling 4GB in dual channel mode (the mobo can support triple, FWIW). After getting an upgrade to 8GB, I noticed that the tech installed a single 4GB stick instead of another 2x2GB.

Though CPU-Z reports that I'm in dual channel mode, I figure that something must be stubbing its toe on a regular basis. I guess the original 2x2GB is probably running in dual channel, but it MUST be going single channel when hitting that 1x4GB stick. I have been noticing that Windows 7 on this box feels quite a bit laggy and slow for such powerful kit, so I'm curious if it has anything to do with this RAM setup? I'm guessing the chipset is smart enough to deal with this uneven arrangement, but given the performance I have to wonder if I'm paying a higher penalty from this than I would if I was just in single channel mode altogether.

I have noticed a few questions regarding single-versus-dual channel modes, but none seem to consider dual Xeon setups.

Any ideas?

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I highly doubt this sort of RAM config will make such a huge difference as to cause Windows to seem laggy/slow. – Karan May 16 '13 at 18:44
Are you using one or two CPU's? What is the path from the CPU's to the RAM? (Wrongly located DIMMs on multi-CPU boards with the memory controller on the CPU can result in two things: 1) Not working (obviously not the case) or 2) The second CPU needing to ask the first CPU for all the data in the RAM, and only the first CPU having access to it). Posting which model motherboard and which RAM sockets are occupied will help us to determine if this is the case. – Hennes May 16 '13 at 20:39
The difference between single and dual channel memory is about 5% on average. (It can do zilch for one program, or boost another program by 100%, it really depends on what the program is doing. Giant memory intensive matrix multiplication which do not fit in the cache will gain much more than a small application. Which is why I bolder the on average). – Hennes May 16 '13 at 20:43
Not asked, bit for completeness and background knowledge: The E5620 is a quad core CPU. The I7 920 is roughly the same and Intel said that their tests showed no significant need for triple channel for those four cores. (It was useful for the later 6 core versions). – Hennes May 16 '13 at 20:45

The difference between dual channel and single channel memory is very small, a few percent at best. You would only notice this difference in memory intensive tasks. In general Windows usage, you wouldn't notice any difference, it certainly wouldn't cause it to be slow and laggy.

Remove the 4GB stick and see if there is any change. If there is then I would imagine it's a faulty ram stick or a damaged memory slot on your motherboard.

share|improve this answer
Faulty RAM should show up on the MCE registers. Removing a stick as you suggested might be easier assuming you have physical access to the server. If not check the values for the Machine Check Exceptions. – Hennes May 16 '13 at 20:48

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