XPS 8940, memory upgrade of 2x8GB

Cas also counts more when all you have is integrated GPU.

I've been experimenting with Ram and watching the scores at user benchmark.

Hi all. Apologies in advance for my long post and many thanks in anticipation for any light that you can shed on my strange and inconsistent experiences in swapping in RAM sticks.

My additional 16GB stick arrived. It looks different to the 16Gb I recently ordered from Dell. The chips look a different design, but they both carry the description:

16 GB 2Rx8 PC4 – 3200 AA

Differences:

the older stick is Made in Korea and the above legend is followed by UB2 – 11

the newer stick is Made in China and the above legend is followed by UB1 – 11

I installed the stick in the one vacant slot (Slot 2). All slots are now filled with Dell upgrade RAM (16 + 16 + 8 + 8 = 48GB in slots Dim One, Dim Two, Dim Three & Dim Four respectively). Note that the slots are as labeled on the mother board and are positioned in terms of distance from the CPU as: Dim 3, Dim 1, Dim 4 & Dim 2 (Dim 3 is closest to the CPU).

Outcome

I turned on the PC. The fans and video card (GEForce) powered up but the PC did not boot up. After 5 minutes the PC powered down by itself and powered itself up again without booting. It repeated this process which I will call ‘power cycling’ several times without actually booting up until I pulled the power plug out.

Testing Four RAM sticks

I tried several combinations of RAM sticks in different slots. All resulted in the same ‘power cycling’ without booting up. (I triple checked every time to ensure the RAM sticks were properly seated)

My conclusion is that 'power cycling' happens when all four RAM slots are occupied.

Q1. Can anyone explain why 16+16+8+8 will stop the PC booting up?

Q2. Is there an optimal way to configure the RAM sticks and Dim slots?

Q3. Do I need to adjust anything (e.g. Bios?) for all four sticks to work?

Additional Testing

1. 1 x 16 GB (Dim 1) worked (single channel and gave a Novabench RAM score of 235 (16,987 MPS)
2. 2 x 16 GB (Dims 1 & 2) worked (dual channel and gave a Novabench RAM score of 327 (31,011 MPS)
3. (2 x 16) + (1 x GB (Dims 1,2 & 4) worked (dual channel and gave a Novabench RAM score of 335 (29,284 MBS)

Final Configuration

Because combination 3 resulted in a slightly higher RAM score and has 40GB instead of 32GB. I decided to stay with this configuration. It’s a bummer that I can’t use the full 48GB I purchased.

Q4. Is combination 3 the right decision?

Additional Thoughts

Also of interest was that the new 16 GB RAM stick would only work if was in Dim 1, not Dim 2

Q5. Is there a reason for this?

Every time I changed a RAM configuration, I would insert the power plug and the PC would power up for around 35 – 60 seconds (it varied) and then power down by itself. I would then press the power button and the PC would boot up ok (of course this did not apply when the PC was ‘power cycling with the 4 RAM sticks)

Q6. Is this normal?

Apologies if my questions seem stupid, but this is doing my head in. Perhaps I should let sleeping dogs lie and be happy with 40GB.......

Cheers & thanks!

Paul

@Leperclown  Did you try resetting BIOS by removing the motherboard battery and pressing/holding the power button for ~30 sec before reinstalling it when RAM is installed in a "no boot" config?

Maybe the new 16 GB module just isn't ot compatible with the first 16 GB module, even though the specs are "right".

Perhaps it's a bad motherboard...??

Try this and see what happens:

DIMM1 16 GB
DIMM2 8 GB
DIMM3 16 GB
DIMM4 8 GB

Yes, I know that's not "normal" but humor me. If it should boot (fingers x'd), check CPU-Z for dual vs single channel mode and RAM speeds.

Mr RoHe, you sir are a genius!

Fiddling with Bios and batteries is well beyond my pay scale, but I tried your suggestion of

DIMM1 16 GB
DIMM2 8 GB
DIMM3 16 GB
DIMM4 8 GB

I must say, I wasn't feeling confident.

However the PC booted up with the four RAM sticks fitted and showed the full 48GB of RAM memory!

 CPU-Z

DDR4        Channel#: Dual      Size: 48GB    DRAM Frequency: 1,463.2 MHz

Novabench 

Total Score: 3,948      RAM Score: 346 (up from 335)  29,251 MBS

Thank you so much for you help and 'out of the box' thinking!

Best regards

Paul

I can't answer all your questions, but can add some insights.

Q5.  My understanding is that when the power cord is reconnected after a modification, the BIOS checks for changes and re-sets itself for the hardware changes.  If there is no change, this doesn't take long.

If you look at some other threads regarding memory in an XPS 8940, you'll find that it is better to put similar memory in odd pairs of sockets - i.e. a Black-White pair next to each other.  I'd expect the PC to work best with the 2 x 16 GB in DIM1 and DIM3 and the 2 x 8 GB in DIM2 and DIM4.  It's not intuitive, but it seems to work.    

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@Leperclown wrote:

Mr RoHe, you sir are a genius!

Fiddling with Bios and batteries is well beyond my pay scale, but I tried your suggestion of

DIMM1 16 GB
DIMM2 8 GB
DIMM3 16 GB
DIMM4 8 GB

I must say, I wasn't feeling confident.

However the PC booted up with the four RAM sticks fitted and showed the full 48GB of RAM memory!

 CPU-Z

DDR4        Channel#: Dual      Size: 48GB    DRAM Frequency: 1,463.2 MHz

Novabench 

Total Score: 3,948      RAM Score: 346 (up from 335)  29,251 MBS

Thank you so much for you help and 'out of the box' thinking!

Best regards

Paul

 

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YEA! Glad that solves the problem, even if we can't explain why it solves the problem on this PC model.

If CPU-Z is reporting RAM speed as 1,463.2 MHz, dual channel, you have to double that because it's DDR RAM. So your RAM is running just about at the max RAM speed (2933 MHz) supported by this system which is great news too!

If your questions have been solved please mark a post in this thread as the solution. And then go enjoy your new toy...!

Sorry RoHe, 1 last question.

I am new to this forum and cannot work out how to mark a post as a solution. There are some marking options ('read', 'new', but nothing for 'Solution'.

Do I just add another post saying the problem is solved.

Apologies

Paul

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@Leperclown wrote:

Sorry RoHe, 1 last question.

I am new to this forum and cannot work out how to mark a post as a solution. There are some marking options ('read', 'new', but nothing for 'Solution'.

Do I just add another post saying the problem is solved.

Apologies

Paul

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This is such a long thread, I didn't remember that you weren't the OP.  Only the OP and Moderators are supposed to be allowed to mark a post as the Solution. So don't worry about it.

The one and only important thing is that you got everything working properly now...

Thks @RaymondGarcia  I bought the crucial spec RAM 8gb followed the steps tried all slots patterns strangely RAM speed reduced to 2400mhz with timing 17-17-17-39 Dual for my i7 10700 latest BIOS 2.1.1. I am unsure whether is the crucial RAM or the MOBO intelligence to select but I can confirm 4x8gb = 32gb is working fine with no issues and minimum performance lost.

I noticed SKHynix has 14 JEDEC crucial 15 JEDEC. The matching JEDEC should #12 1527mhz with timing 21-21-21-49

Anyway I am moving on no luck I guess... thks for all for sharing

I am in the market for a new PC & am considering the 8940 w the 2x8 (16 GB total) Ram config.  But I would like the option of upgrading it to 4x8 (32 GB total) sometime down the line if it is needed.  So, is the consensus that the 4x8 config will work at 2933 MHz as long as you buy compatible Ram & install it in mismatched pairs?  Seems weird to me that this would work, but that is what is posted earlier in this thread.

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@Eagle74 wrote:

I am in the market for a new PC & am considering the 8940 w the 2x8 (16 GB total) Ram config.  But I would like the option of upgrading it to 4x8 (32 GB total) sometime down the line if it is needed.  So, is the consensus that the 4x8 config will work at 2933 MHz as long as you buy compatible Ram & install it in mismatched pairs?  Seems weird to me that this would work, but that is what is posted earlier in this thread.

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Seems to be reproducible, but unexplained, why installing mis-matched pairs allows RAM to run at max speed.

That said, always worthwhile installing them as matched pairs first and checking RAM speed. And if it's not running at max speed, mis-match the pairs and check RAM speed again...

Thanks for your help.  I just did not want to have to buy 2 16 GB sticks to go from 16 to 32 in the future.

I had 2x8GB in my XPS 8940 with a i7-10700, (Dell MICRON MTA8ATF1G64AZ DDR4 3200). I purchased 2x8GB of RAM Crucial (CT2K8G4DFRA32A DDR4 3200) on AMAZON. When I install the 2 new RAM normaly (In free slots 1 and 3), the RAM speed went from 2933 MHz down to 2400 MHz. So, I put the 2 RAM CRUCIAL in slots 1 and 2 and the original RAM Dell in slots 3 and 4 and the speed went to 2933 MHz. I know that's not "normal" but it's works perfectly !

From XPS 8930 Manual:

24 - DIMM3 (black)
25 - DIMM1 (white)
26 - DIMM4 (black)
27 - DIMM2 (white)

From XPS 8940 Manual:

5 - DIMM3 (black)
6 - DIMM1 (white)
7 - DIMM4 (black)
8 - DIMM2 (white)

XPS 8940 does not have the chart showing how to install the DIMMs, but it is the same principle.

So, correct matching is not same color, either black or white, but different color, black and white for each pair or RAM.

But I agree it does look counter-intuitive.

thank you, it works for me too,

XPS 8940 i7-11700, 2*8g stock ram preinstalled in DIMM1 and DIMM2

I purchased another 2*16g Crucial (**8C4LXXCJ), installed in DIMM1 and DIMM2 works, DIMM3 and DIMM4 works

but not work if 4 installed this way:

DIMM1 16 GB
DIMM2 16 GB
DIMM3 8 GB
DIMM4 8 GB

finally follow setting from RoHe:

DIMM1 16 GB
DIMM2 8 GB
DIMM3 16 GB
DIMM4 8 GB

got 48GB work well at 2933 Mhz

don't think to need clear BIOS, but they need to put in the correct slots.