cyrilbrd,

Below is the memory configuration for the xps 8930.

Memory

The XPS 8930 has four DIMM slots. Your computer supports 8 GB, 16 GB, 24 GB, 32 GB, and 64 GB UDIMM DDR4 memory (up to 2400 MHz for i3 processor and up to 2666 MHz for i5/i7/i7k processors).

The following table lists the available memory configuration matrix:

Memory

Although not tested/validated by Dell or listed in the manuals or specifications, another Forum XPS 8930 customer confirmed that 48GB worked;

White DIMM 1 16GB

White DIMM 2 16GB

Black DIMM 3 8GB

Black DIMM 4 8GB

The memory configuration matrix is in error. Memory should be installed in pairs with similar color securing tabs (white or black). Securing tabs for DIMM1 & 2 are white and DIMM3 & 4 are black according to the System-board components diagram in the service manual so the matrix is wrong for 8 GB, 16 GB, & 24 GB configurations. Also the Note is wrong, it should say use slots DIMM1 and DIMM2 for 2 memory modules. Note how the modules are correctly installed by the XPS 8930 forum customer mentioned in Jesse's post.

I can also confirm that not all working configurations are listed. My XPS 8910 came with a single 16 GB module in DIMM1. I upgraded to 32 GB by installing a 16 GB module in DIMM2. None of those configurations are listed in the memory configuration matrix which is identical to the matrix for the XPS 8930 and has all the same errors. Dell has repeated the errors in the service manuals for the XPS 8910, XPS 8920, and XPS 8930. 

Thank you for the reply, Yes I have indeed seen this matrix in the xps-8930 desktop service manual.

I made a mistake in my Original Post, the DIMM allocation is incorrectly stated.

Now if we look at the four memory-module slots (DIMM1 to 4) (and to use the terms of Vic384), from right to left we have:

memory-module slot (DIMM2) (in white)

memory-module slot (DIMM4) (in black)

memory-module slot (DIMM1) (in white)

memory-module slot (DIMM3) (in black)

I received the machine with two 8GB 2666MHz installed in DIMM 1 and 2, could I install two additional 16GB 2600MHz on DIMM 3 and 4?

Or should it be 16GB on DIMM 1 and 2 and then 8GB on DIMM 3 and 4?

Or I should not try to mix RAM as stated above...

Although I don't think it matters I would install the 16 GB modules in DIMM1 & 2, and the 8 GB modules in DIMM3 & 4. I assume 2600 MHz is a typo and you mean 2665 MHz.

Yup, missed that one... should have been 2666MHz.

Thank you for your feedback. Well noted. 

     Just bought a new Dell XPS 8930 and can confirm that the matrix listed in the manual is CORRECT!  Two 8 GB modules in DIMM 1, 2 (White, White) does NOT work - 4 Amber flashes from power button - "reseat memory or bad memory."  Two 8 GB modules in DIMM 3, 4 (Black, Black) does NOT work - 4 Amber flashes from power button - "reseat memory or bad memory."   Only configuration that works with two 8 GB modules is DIMM 1, 3 (White, Black) - boots up showing 16 GB available memory.  Haven't tried DIMM 2,4 (White, Black) config yet.  Verified each 8GB module alone in DIMM 1 - OK.  Either the manual was correct, or Dell has changed their motherboards to match their erroneous manuals!   Apparently, securing tab color pairs isn't always correct.

@DE54  Can you verify that your motherboard matches the picture of the motherboard in the Service Manual on  page 12? Note that in that picture #25 is DIMM1 slot (white tab) and #27 is DIMM2 slot (white tab). The picture also matches the picture that @Anonymous posted. This motherboard layout with the securing tab color configuration has not changed since the XPS 8910 and XPS 8920 and the error in the memory configuration matrix have not changed either.

The other thing you should do is install CPU-Z and look at the Memory tab to verify that your memory pair is operating as a pair in Dual channel mode.

Some motherboard manufacturers do not use different securing tab colors, but those who do, use matching colors to denote matching slots. Having mismatched colors for matching slots makes no sense.

Yes,  identical to your picture.  Dell IPSKL-VM

Two 8 GB modules in DIMM 1,3 slots (white, black) .  Ran CPU-Z and showing 16 GB memory, but single channel?  Ran diagnostics,  ePSA found no issues with DIMM slots, but DIMM 1,2 (white, white) or DIMM slots 2,4 (black, black) keeps giving me 4 Amber flashes - "reseat memory or memory bad." Each memory module works fine in DIMM slot 1.

@RoHe"And if the 2 modules in the pair aren't identical, even if the specs look the same, you won't run in dual-channel mode."

I generally agree it is better if the memory module pairs are identical. My two modules are not identical, the original which came from Dell is a SK Hynix HMA82GU6MFR8N-TF (16GB) and the other was purchased from Crucial Technology CT16G4DFD8213.C16F(16GB) and the specs are not exactly the same, yet they run fine in dual channel mode. One reason I brought memory from Crucial is their reputation for being compatible.