XPS 8940, RAM upgrade, Rank 1 vs Rank 2?

@ecto69 There is an explanation of single vs dual rank here: https://www.oempcworld.com/support/singlevsdualram.html#:~:text=Generally%20Single%20Rank%20Memory%20is,go%20around%20the%20track%20twice.

I had bought my 8940 with 16GB. According to the FAQ, it seemed you might get either (rank) with no choice?

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DK8NX 16GB DDR4, 3200MHz, 2Gx64, Unbuffered, 288 pin, Single Rank, 1.2V, Non-ECC, Non-Encrypted Adata AO2P32NCSV1-BEVS, Hynix HMAA2GU6AJR8N-XN/HMAA2GU6CJR8N-XN, Kingston KDK8NX-MIB/KDK8NX-MIE, Micron MTA8ATF2G64AZ-3G2B1/MTA8ATF2G64AZ-3G2E1, Samsung M378A2G43AB3-CWE/M378A2G43BB3-CWE

C5N22 16GB DDR4, 3200MHz, 2Gx64, 2RX8, Unbuffered, 288 pin, Dual Rank, 1.2V, Non-ECC, Non-Encrypted, Adata AO2P32NCST2-BZ7SHD, Hynix HMA82GU6DJR8N-XN, Kingston KC5N22-HYD/KC5N22-MIE, Micron MTA16ATF2G64AZ-3G2J1, Samsung M378A2K43EB1-CWE

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When I got the option details I complained I wanted Dual Rank. Was told that there was no way to specify and it had more to do with what stock they had.

So when I was ready to move up to 32GB I got 2 16GB Dual Rank RAM from Crucial. Works fine.

I can sell you the 16GB Dell RAM if you want

There are a lot of sites that have 'theories' on which RANK is better. Here are some other than the one listed above:

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https://history-computer.com/single-vs-dual-rank-ram/ 

https://www.cgdirector.com/single-rank-vs-dual-rank-ram/ 

https://blog.memory4less.com/2022/09/16/difference-between-dual-rank-and-single-rank-ram/ 

You can also MIX the ranks, but you might experience some problems.

I first bought a Dual Rank 16GB and put it into the 8940. I had NOT problems, but the RANK stayed at the Single one. I then bought another of the same model and replaced the Dell supplied one and the RANK became Double.

To be honest, I did not SEE any gain overall.

Some say the Memory Controller plays into it, and you have what you have on the motherboard. Can't change it.

Some say using 2 different channels when mixed helps avoid problems and increases speed. I didn't see that either as I tried mixing on the same and different channels and tested.

Some say RAM pairs should be bought together, but I happened to get 2 different 'dates' as I didn't realize a matched pair could be bought.

Overall, I didn't exhibit any problems.

Oh, why did I go to Dual Rank? 2 reasons, one was I wanted 32GB for a game, the other was at one point the Nvidia Lock Up problem on the 8940 was thought to be due to using Single Rank RAM (disproved later).

The ONLY way I knew I actually was running Dual Rank was with CPU-Z on the SPD page:

Thanks I am thinking that buying 2 16GB and replace my current might be the best way to go. and it looks like these are either Dual Rank or Single with no option to choose which, but not sure.

Looks like either dual or singleLooks like CL22 is what I need

MTA8ATF2G64AZ-3G2b1 Micron 16GB

This is my 1 - 16GB ram

Looks Like it is Micron

Yes, matches the FAQ list I posted. Mine is the Micron, Samsung M378A2G43AB3-CWE.

Maybe you only need to buy 1 16GB if you don't care about RANK? Micron makes the Crucial RAM. Crucial is the distributor of Micron.

I had no problems mixing, but you would have less (if any) if the same brand.

Its your money though

got 32gbnew RAM 2x16GB

Replace the Dell 16GB with 2 Crucial 16GB for 32GB total

Worked 100% zero issues, Thank you for all your help.

If we're talking about XPS 8940 then you don't have to "replace" existing RAM but rather add extra modules to existing one since your PC has 4 slots (obviously allocating module pair to right slots). This will land you with 48GB of total RAM where pair of modules will operate in "dual" fast mode and third module will operate at a slower (single) bandwidth, this is called "flex" mode. Fastest (dual) memory region will be automatically assigned for most used data.
I think it is very well described here.

Thanks , Yes my system is the XPS-8940 with a i7-11700 ( when I bought it I did not fully understand the K CPU vers Mine locked and I was wanted leaned toward energy saving)

I did manage to get the best XTU2 benchmark my CPU runs at full speed for like 30 seconds before it drops to 3.5Ghz every test so far has it go to one of the throttling modes (current or power) at least it no longer goes to heat. The DELL original CPU cooler was a joke. 32GB i7-11700 XPS 8940

I was reading about flex mode, but did not fully understand it and was trying to find more info on using dual Channel and Single Channel at the same time. I need to try 48gb setup and do some bench mark tests to see how it works for my usage.

Currently runs in Dual Rank , my original 16GB is Single Rank.

A few things about using Flex.

First is that you have no control of where 'what' is loaded into RAM by Windows. Memory Management loads into RAM as the 'item' is needed'. True, booting process will load first. As programs end, the space is RAM is marked available. Assuming the first Channel is used first and is Dual Rank, it gets loaded then the second channel. So how you add the Dual Rank RAM matters, Channel 1 or 2. After that, what gets put where is up to Windows Memory Management.

Device drivers can be unloaded. Windows generally will first use Memory that is free. Once all used, it looks for deleted/closed program areas in RAM and uses them. If nothing is available, areas not accesses the longest is written to the swap file and that area is used. So, it is possible a loading of a program or device driver could go anywhere.

You testing should also show you how the CPU's Memory Controller works. It appears to be single one for both channels, so it might slow down to Single Rank for all channels. Youe testing should determine if this happens or not?

Of course, Dell never testing a 48GB RAM total, so they consider it 'unsupported'. It should still work, but they never tested that.

You might not even need 48GB's even. Only when 32GB's were to be filled and some had to be written to the Swap file would you gain anything by adding RAM. Hard to actually tell though, other than looking inside the swapfile and see it the contents were changed?

Again, it is questionable if one could tell if you are running with Single or Dual Rank RAM. Performance testing programs could tell the different, but not sure you could in the usage of the PC. RAM access is only part of the overall performance of whatever you are doing.

I don't think it could hurt putting the single 16GB of RAM though. If you are indeed using more than 32GB's of RAM it will stop writing to the Swapfile until you fill 48GB's of RAM and that WILL improve performance for you. However, keeping 32GB's of RAM 'active' (that means all loaded and active programs using RAM) used may not be happening for you? Nor any program or set of programs you have using all RAM even? Possible maybe though. Of course, if you did and filled the Swapfile, you would get an out of memory message, and that is a giveaway you need to either enlarge the swapfile or add more RAM.

Mostly agree with @ispalten , theoretically double-channel region should be filled first as priority by memory management system, only then it goes into single-channel region of addresses (which otherwise would go into swap page file, and we know it's even slower than single-ch ram).

I've also done some benching about a year ago on my older PC after getting current PC and upgrading memory here (so moved DDR4 into older computer and run tests).
It was 48GB in the end but in Dual-channel mode (8+8 GB on first pair, then 16+16 GB in second).
Your case is different (16+16 GB in pair on dual-ch, then 16 GB in single mode)
(Old PC benchmark results below)

Haven't run AIDA64 on existing machine since it normally installs trial (and I don't want excess traces left in a system). but just for comparison 64GB DDR4-3200 with 11th gen i7-11700 on W580 chipset below:

I think AIDA64 is averaging speeds for benchmark from different regions, so you can tell if memory is operating in dual/single/flexi mode based on those benchmarks.

E.g. if it is closer to theoretical limit of your CPU RAM specification and above single channel - then it's flexi-mode (assuming there are sample hits on all regions since I would expect uniform distribution on sampling).
If it is above single-channel speeds and materially below expected dual-channel speeds - then it is flexi mode, if it is slightly below theoretical single - then conclusion is more or less obvious too.
Keep in mind what no-K versions of 11th gen customer cpus are working in gear-2 mode (so either memory controller goes at reduced speed or you get 2T on command rate, gear1 mode only for K grade cpus where you can get full DDR speeds with max memory controller frequency and CR=1T at the same time).


As for throttling issue - we had similar discussion about Dell design in different thread here, it looks like they're optimized for stability as priority 1 (only then performance as P2) and sometimes cheaper models shipped with poor cooling but even if you overcome thermals (temps throttling) you almost immediately hit another wall (power throttling) since there's no much distance between two and design hardly allows to push second limitation (power throttling).

@sam55todd ,

I might not have been too clear in what I was stating.

The real question is performance, that is true, but it is also based on what the single i7 on the CPU Memory Controller will do? Yes, RAM is filled Channel 1 and then Channel 2. Assuming Channel 1 is the Dual Rank, at first you have Dual Rank used and the controller accessing it as Dual Rank.

However, windows fills RAM sequentially until all FREE SPACE is used. As you close a program the space used it marked to be reused. Free space remains as the first choice I recall. So, at some point, something will be in Single Rank RAM.

I don't think the Memory Controller can be in both states operationally at the same time? It would then default to the slower Single Rank access. If so, and it remains in that mode, adding the Single Rank RAM might not be the best thing to do overall?

I can't locate and info on this one way or the other though? It is possible it can work as needed based on the RAM address? Not clear either what happens if it has to due to multitasking the different RAM intermixed either?

In any event, unless one was using the disk (hard disk being even slower than the SSD which is one you'd not want to use for a swap file either) one wouldn't 'feel' any performance different between to 2 ranks overall.