To start, I didn't put this system together 
I bought it used with 3x 4 GB of DDR3 already installed in this configuration.
It has 2x 4 GB sticks of Crucial 1333 MHz RAM that appear correctly spaced for dual channel, then it has one rather random 4GB stick of Corsair 1666 MHz RAM in one of the other free slots.
This is on an MSI 990FXA-GD65 with an AMD FX 8350. All 3 DIMMS are running at 1333 MHz with the same timing and voltages.
I've previously assumed it had the Crucial sticks running in dual channel with the Corsair stick in single channel via Flex mode or whatever it's called, though CPU-Z shows Channel # as Single, so perhaps not. Under SPD it shows the one Corsair stick with 'Ranks' Single and both the Crucial sticks show 'Ranks' Dual - does that mean the Crucial sticks are in dual channel afterall? Is dual rank the same thing as dual channel?
Thankfully the system runs perfectly stable despite this configuration and I'm not having any unexpected performance issues that I can tell. In games the GPU is usually at 100% and CPU at ~60%.
Here's a 3Dmark result if that's any help.
https://www.3dmark.com/spy/4582997
If it is all running in single channel, would there be any noticeable performance gain if I was to replace the RAM with, say, 4x 4 GB identical 1666 MHz DIMMS?
I bought it used with 3x 4 GB of DDR3 already installed in this configuration.It has 2x 4 GB sticks of Crucial 1333 MHz RAM that appear correctly spaced for dual channel, then it has one rather random 4GB stick of Corsair 1666 MHz RAM in one of the other free slots.
This is on an MSI 990FXA-GD65 with an AMD FX 8350. All 3 DIMMS are running at 1333 MHz with the same timing and voltages.
I've previously assumed it had the Crucial sticks running in dual channel with the Corsair stick in single channel via Flex mode or whatever it's called, though CPU-Z shows Channel # as Single, so perhaps not. Under SPD it shows the one Corsair stick with 'Ranks' Single and both the Crucial sticks show 'Ranks' Dual - does that mean the Crucial sticks are in dual channel afterall? Is dual rank the same thing as dual channel?
Thankfully the system runs perfectly stable despite this configuration and I'm not having any unexpected performance issues that I can tell. In games the GPU is usually at 100% and CPU at ~60%.
Here's a 3Dmark result if that's any help.
https://www.3dmark.com/spy/4582997
If it is all running in single channel, would there be any noticeable performance gain if I was to replace the RAM with, say, 4x 4 GB identical 1666 MHz DIMMS?
