http://www.dell.com/downloads/global/products/optix/en/optiplex-990-tech-guide.pdf

 Core I 3000 series does not appear to be listed for

INTEL Q67 Express Chipset / Intel® HD Graphics 2000

SFF HAS 4 Slots and USFF only have 2 ram slots. So 8 or 16 gigs is max not 32 or more.

http://www.crucial.com/usa/en/optiplex-990-small-form-factor/CT7366077

Max Dimm Size is 4 gigs not 8 or 16 gig dimm.

LGA1155 is a VERY specific Socket.  Fitting into the socket and compatability are not one and the same thing. The Q67 Lists the following.

I dont know about you but this helped me out with my motherboard purchase thank you 

You can put 32GB ram in 990 SFF as proof on a sold eBay pc.

this is commonly seen in optiplex where user can successfully upgrade ram to 2x Dell spec max.  It is doable although considered nonstandard by Dell and outside the scope of Dell.

Hi Red

Do u think it will work on Core i3 as well?

Thanks.

Memory support is the chipset's job. The processor "talks" to the memory through the chipset. So whether memory works or not is not dependent on the processor model (so long as the chipset supports it).