hynix is dual rank :
https://www.compuram.biz/memory_module/hynix/hmt125u6bfr8c-h9.htmSamsung is single rank it says so in the title 1Rx8
i wrote it wrong in the previous comment ... one channel is slots 0 and 1, the other is slots 2 and 3 ... so if you want dual channel with two sticks, you put rams in 2nd slot of each channel, which would be 1 and 3 (furthest away from cpu socket, in theory you get better signals and potential for higher clocks and lower timings if the sticks are closer to the termination resistors)
so what i was thinking on saying is that if two sticks are dual rank and the other two are single rank, i'd try to put the two dual rank on one channel (2nd channel, slots 2 and 3) and the two single rank on the other channel, in the hope that at least one channel can gain some performance increase by using two ranks in a more efficient way.
It probably doesn't matter on a system so old, or probably the memory controller doesn't implement this, but on more modern systems like let's say socket AM4 from AMD, the memory controller can gain a bit of performance with dual rank sticks by issuing commands to one rank and do something else with the other rank while the stick is busy with first rank.
It's something like this, in a simplified way ... the memory controller sends a request (an address) to read data from or write data to, then it takes some cycles for the ram chips to be ready to read data from, and once they're ready they can send data from that address in a burst .... well the controllers can send a "get ready command" to both ranks, switch to one rank and read the data and in the meantime the other rank is ready to transfer the data and the controller can switch rank and start receiving it, instead of switching rank, sending get ready command, waiting and then receiving ... it's a few nanoseconds of time saved.
If you mix single rank and dual rank on a single channel, this scheme may not work, depends on the controller I guess.
I don't remember if it was during the DDR2 times or also was the case with DDR3 but some intel chipsets (when they still contained the memory controller) couldn't handle ram sticks made with 4 bit wide chips, while amd controllers could tolerate a wider range of memory arrangements
for example
https://www.ebay.com/itm/266454765280 and
https://www.ebay.com/itm/224578744702 , these won't work with some (if not all) intel systems.... while they'll work in AMD systems. that's why they were often cheaper sticks or sold only to OEMs.
Usually ram sticks are made with 8 bit wide chips, so you have 8 chips x 8 bits = 64 bit wide, so if you have a ram stick with 16 chips, it's gonna be dual rank, usually one rank per side. But the ram sticks in the link above use 4 bit wide chips, so all the 16 chips on the stick form a single rank.
They also make 16 bit wide ram chips, where you only need 4 chips to get the 64 bits it's quite common in laptop ram ... here's an example
https://www.amazon.com/3200MHz-PC4-25600-260-Pin-Notebook-M471A1G44AB0-CWE/dp/B08QRZX7B4Some "value" ram sticks were made for desktops as well, and usually used by OEMs to cut costs.
Example :
https://www.amazon.com/Crucial-2x8GB-Desktop-Memory-CT2K8G4DFRA32A/dp/B08C53LL9J/ - there's nothing under the label, only 4 chips on the stick.
These are usually slower than x8 ram sticks, LinusTechTips made a video explaining why, I don't remember the reason off the top of my head right now
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