Frogggy,

I have no personal experience with this system so please take this with a pound of salt, but the Crucial website shows a maximum of 64GB RAM in 4 DIMM slots That would be a max of 16GB per stick. 

https://www.crucial.com/compatible-upgrade-for/dell/precision-workstation-3620

Intel also shows that your CPU supports a max of 64GB.

https://ark.intel.com/content/www/us/en/ark/products/88196/intel-core-i7-6700-processor-8m-cache-up-to-4-00-ghz.html

Randy

PS, The RAM speeds supported by your CPU are listed in the Intel link above.

Hi @Frogggy,

I think you meant 2,133MHz and not 2,166MHz?

From the Precision 3620 Tech Guide, max supported RAM speed is 2,400MHz.

Thank you very much to both of you for your answer and help!

Of course you are right, I ment 2133 mhz and not 2166mhz!

Well, the intel link says the processor only supports 2133 mhz DDR4. The other say it could support 2400mhz.

Since the diffrence in performance won't be too big I guess, I will just buy another 16gb @ 2133 mhz and not a new 32gb @ 2400 mhz.

Should be the best Price/performance result.

Thanks again for your help!

I searched so long to find valid information from dell but i couldnt find anything in the manual about that.

And you're right - manuals certainly aren't the most helpful.  I could get some tech guides from Dell, but not all, leaving me to think there wasn't any for some PC's and workstations.

Here's where I've been getting some tech guides from, and so far, they've been a trusted source.  They just make you verify you're a person before downloading.  https://www.manualslib.com/manual/1304399/Dell-Precision-3620.html 

Also noted, which I think I've should've noted before, the screengrab I gave wasn't a part that says your CPU supports a max of 2,133MHz RAM speed.

A couple of RAM tips:  Crucial is guaranteed to work Dell's, have a lifetime warranty,, but are a little pricey.  To save money on a not so new Dell (I don't consider old either), I use A-Tech RAM, which also has a lifetime warranty.

By my experience, Dell never supports RAM clocks higher than Intel CPU specs declare.

If you want more, you need a custom, probably SuperMicro-based machine, but I will tell you, it is another headache.

That does not mean you should not purchase faster RAM. Faster ram is just more reliable on slower clocks, especially when you populate all the slots.

P.S. Crucial is Micron, and Micron is the best, anyone can offer. They have the honest declared specs and SPD configuration, and never fail in most, even worst designed boards.

Does it matter if different RAM capacities are installed in the RAM slots?  For example, there are 4 RAM slots on my motherboard and two of them are filled with 8gb RAM cards totaling 16gb.  If I added a 16gb ram card in each of the two remaining RAM slots would that cause a compatibility issue?

@Frogggy 

None of the precision models support XMP so any ram other than 2133 2400 2666 1.2v Jedec is pointless. The cpu determines the ram speed.

DDR4-2666 • CL=19 • NON-ECC • UDIMM • 288-pin • 1.2V • 2Rx8  • PC4-25600

PC4-25600 3200 2666 2400 2133 1.2v B09KP21Q1F

$30 or less per 8g dimm

@Dustpan135 gave a chuckle with the nickname.

@Dustpan135 also asked if RAM capacities can be mixed.  Some people do it and it works, but no guarantees.  If you try it, make sure the RAM is returnable just in case.  Make sure ALL other specs are the same - mfr., speed, volts, either ECC or non-ECC according to the CPU you have.  That increases the chances of it working.

With the 3620 being introduced in 2016, I'm not saying it'll for sure be cheap, but sometimes there's good deals on RAM on older/somewhat older machines.  A-Tech is a brand I've used for years and had a lifetime warranty.  I mention in case you might consider replacing all of the RAM so it's all the same.

Thanks for your advice.  I think I will go the safe route and order 4 new RAM cards from the same manufacturer and with the exact same specifications.  I will also order A-Tech.

Does mfr. stand for manufacturer?  From my command line it lists my manufacturer as 80AD000080AD.  Is that info that I should use in finding the right RAM?  Or are you saying that I shouldn't mix A-Tech with Crucial or some other brand?

My speed is listed as 2133 MT/s.  When I shop online I see this often listed:  PC4-17000 2133 MHz.  Is that compatible?    Will a 2400 or 2666 work just as good as a 2133?

When you say " either ECC or non-ECC according to the CPU you have."  From my command prompt it states:  Type Detail:  Synchronous Unbuffered (Unregistered).  From shopping online I saw this listed:  Non-ECC Unbuffered.  Do Non-ECC Unbuffered and Synchronous Unbuffered (Unregistered) mean the same thing?

Thanks for liking my name.

If I were you I would not go any higher than DDR4-1866/2133, DDR3L-1333/1600 @ 1.35V. That's just the specs and Dell's motherboard supported specs that I would stick too.