Dell XPS 8940 RAM Upgrade

Hi

The Dell XPS 8940 uses four UDIMM DDR4 slots and supports up to 128 GB total. Dell lists supported sizes of 4 GB, 8 GB, 16 GB, and 32 GB per slot, with dual-channel operation and speeds of 2666 MHz or 2933 MHz depending on the processor. dell

Supported configurations

Dell’s documented memory configs include 8 GB, 16 GB, 32 GB, 64 GB, and 128 GB combinations, using either matched pairs or four-module setups. The machine is shipped with 3200 MHz memory, but it downclocks to 2666 MHz with Intel Core i3/i5 CPUs and to 2933 MHz with Intel Core i7/i9 CPUs.

5. memory-module slot (DIMM3)

6. memory-module slot (DIMM1)

7. memory-module slot (DIMM4)

8. memory-module slot (DIMM2)

Daft idea, you may be mis-matching the modules.  The picture suggests an odd arrangements to my eyes.

HOWEVER I do acknowledge that you have tried 4 identical modules.

I would clear the cmos after fitting and re-boot and allow the BIOS to recognise whatever is installed, and perhaps select a speed setting.

BUT I cannot see that you are doing anything wrong.

Very odd?

I had originally 16GB and added 1 16GB Crucial RAM and it works fine as dual Channel even.

Doesn't matter the speed of the RAM, Dell will use it at 2666 speed if you CPU is not an Intel i7/i9:

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The Dell XPS 8940 has four UDIMM slots that support up to 128 GB of dual-channel DDR4 memory. While the motherboard can handle faster speeds, system limitations cap the memory clock at 2666 MHz for Core i3/i5 processors and 2933 MHz for Core i7/i9 models.

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More than likely you might have a problem with the sockets or you are not using the correct pairs? Since you are using all slots now, it might be the pairing of the slots. Or it more than likely that the configuration of 96Gb's just will not work. 

See this link for tested memory XPS8940 configurations --> https://www.dell.com/support/manuals/en-us/xps-8940-desktop/xps-8940-setup-and-specifications/memory?guid=guid-e9d2ea83-38a4-431d-803c-96d63c1dbc34&lang=en-us

Oddly enough, 4 x 32Gb's IS approved and tested? Sort of points to the 32Gb cards or one of them might be defective.

I would test the 32Gb cards... use only 2 and see if it boots... doesn't, one those cards is bad, and test cards individually. If they were, use the other 2. Make sure the correct channel 1 and 2 slots are used.

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Always the same size RAM in the same Channel.

always try Dell oem ram

Dell validated 2x32 gb below

732YD 32GB DDR4, 3200MHz, 2Rx8, Unbuffered, 288 pin, Dual Rank, 1.2V, Non-ECC, Non-Encrypted:

Hynix HMAA4GU6AJR8N-XN/HMAA4GU6CJR8N-XN,

Micron MTA16ATF4G64AZ-3G2B1/MTA16ATF4G64AZ-3G2E1,

Samsung M378A4G43AB2-CWE

@anne_droid​ Thank you for this information. I believe that my first problem was that I tried using two new 32Gb cards and leaving two of my original 16Gb cards in as well. I now know from Dell that using the old cars with new cards could be a problem. The second attempt with 4 new cards could have been a defective part but these were off-brand cards from Newegg and I did not want to mess around with them. I have gone with 4 Crucial 32Gb cards recommended by Dell and I hope that works. I should know in a week or so. Again thanks for the comments.

@ispalten​ Thank you for this information. I believe that my first problem was that I tried using two new 32Gb cards and leaving two of my original 16Gb cards in as well. I now know from Dell that using the old cars with new cards could be a problem. The second attempt with 4 new cards could have been a defective part but these were off-brand cards from Newegg and I did not want to mess around with them. I have gone with 4 Crucial 32Gb cards recommended by Dell and I hope that works. I should know in a week or so. Again thanks for the comments.

@redxps630​ Thank you for that information.

You can buy Dell oem compatible ram on line using memory maker model number and often find good price.  

The Dell XPS 8940 can be a bit particular about memory upgrades. Mixing the original Dell RAM with new modules often causes compatibility issues, so using a matched kit is the right approach.

A few things to check:

• Make sure all four modules are DDR4 UDIMM (non-ECC, unbuffered).
• Verify that your specific XPS 8940 configuration and BIOS support 128 GB (4 × 32 GB). Some earlier configurations have lower supported capacities.
• Install a matched kit from the same manufacturer and model number rather than mixing different brands or kits.
• If your CPU officially supports DDR4-2933 or DDR4-2666, installing DDR4-3200 is usually fine—the memory should downclock automatically. The speed itself is typically not the reason the system fails to boot.
• Ensure the BIOS is updated to the latest version before installing the new memory.

Many users have had success with Crucial Pro, Kingston Fury Beast, or Corsair Vengeance LPX 32 GB DDR4 UDIMM kits, provided they're installed as a complete matched set.

@Adaeze2​ Thank you for this information. 

Based on Dell recommendations my most recent attempt was with 4 Crucial DDR4-3200 UDIMM 1.2v CL22 32GB cards.

I initially had 4 16GB cards that came with the new computer.

I realize that I cannot combine any new memory cards with my older (initial) cards.

I installed 2 of these Crucial cards into the white slots (1 & 2) and then tried to start the computer. Nothing not even a flicker on the monitor.

I installed the remaining 2 cards into slots 3 & 4 and again tried to start the computer – nothing.

I re-installed the 4 16GB cards and started the computer.

HOW CAN I CHECK THE BIOS ON MY PC?