Hi alaaanbar,

Thank you for reaching out to us. We will be glad to assist you with the query.Kindly private message us the service tag of the system, so that we can check the system configuration and assist you accordingly.

No you cannot mix RANKS and Density.

@alaaanbar 

I have a 790, and I think it is very similar to 990. I use two modules which are single rank (4GB each) and two modules which are dual rank (8GB each). For total of 24 GB.

I think you will have no problem, but don't use buffered or registered memory (mostly server type memory, which not good for your 990).

Hi alaaanbar,

The system support dual channel mode. If the channels do not match or if the system has only one DIMM installed, the system memory operates in single-channel mode or in dual channel asymmetrical mode. The system works normally in single-channel mode, but then you lose the benefit of increased memory throughput.

Please private message us the system service tag so that we can check which version of Optiplex 990 you are operating.

Regards,

Akshatha

Dell company only sell computers, but they don't support costumers

Thanks for your answer,

I asked technical support in Holland even in USA, they don't know anything about Dell OptiPlex 990 or any other Dell versions

So, I’m allowed to use 2Rx8 on Dell OptiPlex 990

Thank you very much

doesn;t need all of these stories,

Optiplex 990 desktop are all same

my questions are very clear

M I able to put 2Rx8 pc3 on Dell Optiplex 990?

Yes or not.

if you have no idea, please be clear as Holland tech support.

they told me we have no idea ask Dell USA branch or go to computer tech shop.

I don't understand, 

What do you mean by:  the system service tag so that we can check which version of Optiplex 990 you are operating.

It's Optiplex 990

I don't know where can I find any info about the pc, 

I follow youtube dell tech

https://www.youtube.com/watch?v=sDPVSHHN-SY

Then I went to this site

https://www.dell.com/support/home/nl/nl/nlbsdt1/

Then it took me to this site

https://www.dell.com/support/home/nl/nl/nlbsdt1/eula/scan?scanType=TMC&appName=home&cancelUrl=https://www.dell.com/support/home/nl/nl/nlbsdt1&returnUrl=https://www.dell.com/support/home/nl/nl/nlbsdt1/product-support/servicetag&intent=

I couldn't find any thing about the pc

I called Dell tech support. I was waitng for more then two hours on the phone, then the manger tech of Dell Holland told me that Dell has no idea about any thing about Dell optiplex 990 and he adviced me to contact USA

long time ago I bought Dell laptop, I had same trouble with Dell tech support, not only me everybody has same problem with dell tech support, 

Dell only sell computers, but it doesn't support custmors

i will never buy dell product any more

Hi alaaanbar,

You can private message the service tag. As informed earlier the system support dual channel mode. If the channels do not match or if the system has only one DIMM installed, the system memory operates in single-channel mode or in dual channel asymmetrical mode. The system works normally in single-channel mode, but then you lose the benefit of increased memory throughput.

I found the sevice tag,

so, how can I send it to you?

At this moment I haven't recieved any clear answer about my questions,

Hi, please private message the service tag let us check the system configurations and proceed further.

The ram is VERY specific.

16 gigs is max

Single or DUAL rank ram is fine

QUAD RANK Ram is not ok

ECC is not ok

Buffered / Registered Ram is not ok.

Spec:

LOW DENISITY  DDR3 PC3-12800 • CL=11 • Unbuffered • NON-ECC • DDR3-1600 • 1.35V • 512Meg x 64 • 

https://www.crucial.com/usa/en/optiplex-990-desktop/CT2348234

@alaaanbar 

Yes, 2Rx8 is OK. Use regular unbuffered dimm modules, not server memory (registered, ecc, etc.) ... those may not work.

Speed step gave you the answer to your question. I tried to boil it down to a simpler level. If it still doesn't help you, perhaps a local computer repair shop in netherlands might be a better choice for you. It may just be a language barrier problem.

Good luck.