Mismatched channels on X79 platform

[NiHaoMike]

I ordered 32GB (4x8GB) of RAM (need it to run VMs - 16GB isn't quite enough), of which 1 of the 4 DIMMs was defective. I have arranged with the vendor to get it replaced, but until it arrives, I'm running my PC with three channels, putting one of my existing 4GB DIMMs in storage for now.

Am I correct in assuming that if I did leave that 4GB DIMM installed, the system would switch into the really slow single channel mode? Or would it do quad channel for the first 16GB and triple channel for the remainder?

 

[Woomack]

All depends from board. In theory quad should run in:
1|3|5|7_cpu_8|6|4|2
or
1|x|5|x_cpu_x|6|x|2
in real on some boards it can work also in:
1|3|x|x_cpu_x|x|4|2

Simply you won't know until you test it but 7 modules should give you 3 or 4 channels.