Some time ago I built a PC with 8 GB RAM (DDR4 2666MHz DIMMs) since I did not have enough money to go for a 16 GB kit.
Later, I realized 8 GB was holding me back from doing a couple of things and went with the cheapest upgrade path available to me, which was buying a single 4 GB stick and adding it to my current setup. Unfortunately, the 8 GB kit I bought was from Corsair, and they did not sell a 4 GB stick by itself, so I had to go with a different manufacturer. I went with Crucial, and tried to match up the speed (obviously) as well as timings as best I could, although IIRC it wasn't quite perfect.
From research, I concluded this was probably going to cause me to revert from dual-channel mode to single-channel mode, which I reluctantly accepted as a compromise, since I doubt I'd see a noticeable drop in performance but I'd definitely benefit from the extra 4 GB of RAM.
However, after getting everything installed, I was greeted with a message from my BIOS to move one of the sticks to a different slot. I did, and still got a message. This time, it was to move the stick from the slot that it was in to the slot... that it was in, which continues to show up to this day. I chuckled at this and went into the BIOS to make sure the speed and timings were set up correctly, then loaded up Windows Memory Diagnostic to make sure it was all good to go. It passed and I checked various locations in Windows and everything showed up as 12 GB of available RAM. Then, I downloaded CPU-Z and ran the 64-bit version of the program. To my surprise, it detected my memory was running in dual-channel mode. After further research, I verified this with
wmic memorychip list full and found that two of the sticks (which were the renegade Crucial and one of the Corsair) were running in dual-channel mode as indicated by
InterleaveDataDepth=2, while one of the sticks (the odd Corsair one out) was running in single-channel as indicated by
To illustrate my setup further, I'm using an MSI H370M BAZOOKA with the memory modules installed like this:
Crucial Corsair Corsair Empty Slot
Going from research telling me that memory and channels are fairly sensitive and that my results shouldn't be possible outside of a specific subset of cases, I'm curious why this is working, and how. I have actually been using the system for a good while like this (and breached the 8 GB mark of used RAM multiple times if it matters), and came across a few things that reminded me of my setup. I'm still pretty confused about this. I did come across Intel FleX, but I'm having trouble understanding if it fits into my situation or what is happening here, exactly.