XPS 8910, why ship ONE 16GB instead of TWO 8GB?

You are right, it is lame. Many have complained over the years. Dell has been listening (at least for high performance machines) and DIMM-count is sometimes specified now on sales-config-page .

However, what is done-is-done . I would not waste money swapping 16gb for 8+8gb on this older machine.

Dual-channel is faster, but only slightly. Plus, you would have to be really using machine hard to realize any perceivable gains.

I would guess that if the 2 x 8 GB RAM modules were not in stock then 1 x 16 GB was picked instead...but that is a huge guess and I agree that 2 x 8 is required for dual channel operation. I believe that Crucial RAM you posted is the same as the specified RAM here.

And FYI, I have seen new systems with an M.2 NVMe/'PCIe SSD and a hard drive and yet the OS is installed on the HDD and not the SSD so go figure.

My XPS 8910 also came with one 16GB memory module and am happy it did because I only had to buy another 16GB memory module from crucial.com to have 32GB total memory. As an added benefit it now runs in dual channel mode. If it came with two 8GB modules I would had to buy two more 8GB modules and use up all the memory slots. Now I still have two free memory slots.

Also note that the original configuration (one 16GB module) and the current configuration (two 16GB modules) are not listed in Dell's Memory Configurration Matrix but it works.

check out the manufacturer

Hynix

Well I just solved my own problem

Best Buy had Corsair DDR4-2400 RAM on sale - why do they sell old slow memory ?

So I replaced the ONE 16GB stick at 2133 for TWO 8GB sticks at 2400mhz

not sure of the MAX speed on the motherboard

Here is my result

new memory

I can't see your pictures yet until they are approved, but my experience and what has been reported in this forum is that the Dell BIOS sets the memory speed based upon only the SPD speed. The XPS 8910 does not have the capability to read and use the memory's XMP (Extreme Memory Profile). I have not seen any reports here of memory in the XPS 8910 running faster than 2133 MHz which is the specification for this computer. You can see the memory speed if you go to Task Manager, Performance tab, click on Memory, and look in the lower right. 

The pictures I posted show 1200mhz in dual channel mode = 2400

That is with two 8gb ram in the white memory slots

I wonder if the motherboard can handle 2666mhz ?

task manager

I don't know if the motherboard can handle 2666 MHz but the Corsair memory I looked at that had a test speed higher than 2400 MHz had a SPD speed of 2133 MHz so that Corsair memory will not run higher than 2133 MHz on that motherboard. Crucial memory may work since some in this forum have used Crucial memory at that speed in the XPS 8930.

They are Corsair Vengence with a heatsink 2400mhz two sticks of 8gig DDR4-2400mhz

I paid 55 dollars

You can see in my pics the old shows 1066mhz  / 2133

and the new shows 1200mhz / 2400

Anyone here with a XPS 8930 ? run CPUID and post your ram speed

Don't know what RAM speed on the XPS 8930 has to do with RAM speed on the XPS 8910, but here's CPU-z for my XPS 8930 with 2x 8 GB of 2660 MHz RAM:

Thanks for the pic and help all...

hmm I noticed your Northbridge NB frequency is different than mine

Anyway My XPS 8910 (2017) PC takes 14 seconds to boot. It used to take 21 seconds

All that speed comes from having memory in dual channel