XPS 8940, four 8GB Crucial ram, no boot

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@Tesla1856 wrote:

One answer is to just run 2 (exactly matching) DIMMs (in one Memory-Bank for Dual-Channel-Mode). And then, you populate the other Memory-Bank. Memory bank slots have matching-colored hold-down clips.

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But that's not the case with the XPS 8940 (and apparently also not for XPS 8950).

To use different pairs of RAM in the XPS 8940, you have to put each pair in slots with different color retention clips, which @DellDeleted and XPS 8940 users in other threads have found out, the hard way.  Otherwise, this PC won't boot.

And yes, this totally violates the "norm" for RAM installation .I have asked for an explanation, but...

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@RoHe wrote:

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@Tesla1856 wrote:

One answer is to just run 2 (exactly matching) DIMMs (in one Memory-Bank for Dual-Channel-Mode). And then, you populate the other Memory-Bank. Memory bank slots have matching-colored hold-down clips.

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But that's not the case with the XPS 8940 (and apparently also not for XPS 8950).

To use different pairs of RAM in the XPS 8940, you have to put each pair in slots with different color retention clips, which @DellDeleted and XPS 8940 users in other threads have found out, the hard way.  Otherwise, this PC won't boot.

And yes, this totally violates the "norm" for RAM installation .I have asked for an explanation, but...

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Best I can tell, they are purposely using DIMMs with different Rankings. I suspect one or both Memory-Banks are falling-back to Single-Channel mode.

Either that, or maybe the slots have been incorrectly color-coded by Pegatron.

If you had a machine available, (and some properly Spec-ed and Rank-ed DIMMs) ... it would be fairly easy to figure out ... looking at BIOS, ePSA,  and PassMark's MemTest86. Finish-up with CPU-z in Windows. 

I have wondered if the slots are incorrectly color-coded, or maybe the motherboard layout is wrong...

Other users who used this same solution all report that CPU-z says Channel #: dual. Since both banks have the same, but mis-matched pairs of modules, I'd expect it to say "single", because I wouldn't expect one mis-matched pair to be dual channel and the other identically mis-matched pair be to be single channel.

I had the exact issue. Then, after much searching, I came across your post. I tried it as a last hope and, it worked? Amazing. Something that theoretically should not work does.

Thanks!!

@Knash63  Glad that helped you too!

Never gotten an explanation why this odd way of mixing RAM pairs works, but at least it's an easy solution...

I wanted to add to this thread that I also was able to install 2 8GB RAM sticks, only after moving the stock ones to one side (one using black clips, the other using white clips).  I installed Crucial brand memory, after using their site to look up their compatible version numbers.  Nothing fancy.

Now I have 32GB that is recognized as dual channel.  Seems to be working.

FWIW, on my 8950, CPUz shows mem in slots 2 and 4 but they are in the clearly labelled slots 1 and 2 (white).

I've seen this with other boards too so not so sure I trust CPUz over the board itself.

Also, system builders always have been aware that sometimes you have a certain logic on installing mem modules like larger ones first so maybe it's similar to this due to the design of the module.

So, now I'm just curious on why CPUz isn't showing dual in the channel # status.

I seriously doubt Dell shipped this 8950 in non-dual channel mode.

This must be how CPUz reports it now (it seems to have changed).

It's showing 4 x 32 which seems to indicate 2 x DDR5 modules.

Still, CPUz does get the slots wrong but that is nothing new.

I did check my other older systems with this CPUz and they do show dual or quad for the memory and interestingly enough, my Intel board has the same showing mem slots 2 and 4 are in use but the board says 1 and 2.

It must be a DDR5 thing (the 4 x 32 vs dual or quad for older DDR).