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.