I know this happened with another user on the forums here. They installed another kit of Patriot PVS34G2000LLKN and the SLI memory was not detected. Although they installed the same part number the memory specs were different, one kit was 1.7 to 1.9 volt memory and the other was 2.0 volt memory.
 
I am running on the P10 bios with 790I Ultra SLI mobo. I have 8 GB of PVS34G2000LLKN Patriot 1.7 to 1.9 volt memory and it shows up as SLI enabled.
 
My guess is the BIOS or some minor change in memory specs between the different sticks may be causing this. I would suggest you try the P10 BIOS and see if it resloves the issue. If this does not work themn I would contact the memory manuffacturer and ask them if there were any discrete differences between the two EPP 2.0 memory sticks you are running. Something may have changed which was not significant enough to list on the memory specs. 
 
Another thought would be to clear your BIOS, per mobo manual directions, if the P10 revision does not resolve this and see if that fixes the issue.
 
EDIT: I am thinking you can see mobo drivers in system info within the nvidia control panel. It has been a while since I looked at this and I could be wrong but I know many of the Nvidia drivers are listed there.

Just manually define the memory settings in the bios and your set.
 
Ive never trusted the Spd detection as it often sets the latencies wrong anyway.

Are you modifing BIOS through a windows program? To see all drivers and current software these will work 
Download "AIDA64" or "Advance system care" by IO BIT, both are free for 30 days, I recommend AIDA64

I have 4 stix of EPP memory installed and I had the same issue going from 2 stix to 4 stix of the same memory. For some reason after I installed the extra 2 stix the bios reverted back to disabled and my memory timings were set back to Auto. Once I manually set my timings and made sure that EPP 2.0 memory was also enabled, the post screen then showed I had EPP memory enabled.
 
So in my opinion you are both right!! 

raguza123

I had SLI ready ram, It was OCZ, the only thing with with enabling EPP, timings are already set, the ram will run faster than the FSB, I just didn't look into it to see if I can modify my FSB settings, I OC'd it and  I was able to get it up to 1800mhz, then I backed it down and it failed. so much for OCZ quaility.   Had to RMA it and it's EOL ram. I had to find out OCZ doesn't play well with the 790i chipset.
OCZ 3N 1800SR4GK PC3 14400 Nvidia SLI ready Edition

If you are running linked and synched you will not have the problem with RAM running faster than FSB. My memory is 2000MHz memory at its normal speed. In my case the memory has been under clocked back to 1333MHz as a result of running it linked and synched.
 
Not pointing fingers at anyone here I wanted to make this general comment. I have a feeling that many of us sometimes return memory which is actually good because we run into things which make us feel the memory has failed to live up to its expected result. I nearly did this myself with some RAM not long ago when it was erring in memtest+ 4.10. After 2 days of off and on playing around with settings I finally figured out what was wrong and it turned out to be BIOS settings for SPP voltage set to low with P1 and P2 enabled.
 

raguza123Are you modifing BIOS through a windows program? To see all drivers and current software these will work Download "AIDA64" or "Advance system care" by IO BIT, both are free for 30 days, I recommend AIDA64

 
I assume you were referring to my posting up the NTune BIOS windows. I will never use a software based utility to set my BIOS settings for one simple reason. Too many others have documented problems in the past with windows based programs when changing BIOS values. The only reason I used this here was to show current settings in my BIOS with hopes something might stand out which would help clarify this EPP 2.0 issue when memory is maxed on a mother board. (As an aside the act of installing some of these types of programs can create issues even if they are not used. Since I plan on wiping this install of my windows soon I personally did not mind taking the chance. I would not suggest to anyone that using a windows based BIOS tuning program is a good practice, it needs to be looked at as a personal and informed choice after understanding the potential for problems.)
 
I 100% agree AIDA64 is not just great it is wonderful for any enthusiast to have and use frequently. That is why I purchased my copy of AIDA64. Now I have full access to all the settings and other values it is designed to display.

When you enable EPP, you are not able to link and snyc memory to the FSB, I tried it, and as far as my memory, it was tested with memtest and it failed, sorry I guess 15 yrs working on pc's I don't know anything, I'll shut up

duntless

raguza123

When you enable EPP, you are not able to link and snyc memory to the FSB, I tried it, and as far as my memory, it was tested with memtest and it failed, sorry I guess 15 yrs working on pc's I don't know anything, I'll shut up

Well the interesting thing is, I couldnt find EPP anywhere in my BIOS. What does it stand for by the way? I read my manual, and the first entry in the memory settings is the SLI Memory setting that used to let me enable and disable. Its currently set to disabled and wont let me change it. Lettering appears blueish transparent like the other unchangeable fields.

Duntless,
Does your memory say EPP 2.0 Ready on it or SLI Ready? If your not sure call the manufacturer and ask them if it is EPP 2.0 ready memory, they will certainly know the answer to that.
 
Based on your saying you used to see the EPP setting in BIOS I assumed your memory is EPP 2.0 Ready have you by chance changed your memory since the time you have seen this designation in BIOS? 
 
As for what Epp 2.0 does go take a look at this Nvidia link where it is completely explained in the PDF.
http://www.nvidia.com/docs/IO/52280/NVIDIA_EPP2_TB.pdf

raguza123

When you enable EPP, you are not able to link and snyc memory to the FSB, I tried it, and as far as my memory, it was tested with memtest and it failed, sorry I guess 15 yrs working on pc's I don't know anything, I'll shut up

Raguza123, I do not know if you were directing this toward me or someone else but I did want to answer your concern in case it was a result of something I said.

Let me apologize for my incorrect usage of the word enabled when I should have used detected instead. My discussion here has been over BIOS detecting EPP 2.0 memory when the motherboard is fully loaded with memory.
 
If I somehow implied you lacked knowledge that was not my intention. We all have something to contribute and I learn from each person who adds to the discussions here. There is nothing you have said which causes me to believe you do not know what your talking about.
 
EDITED: I can also understand how your memory may not have passed memtest+ (looks like your memory did have a probelm). I was not trying to say you returned good memory. I just made a general comment about what I see on the boards here and at other sites where memory is returned without considering other causes. That comment had nothing to do with your statement, it was simply a passing thought as I was writing which is why i began the sentence by saying "Not pointing fingers at anyone here".
 

The Memory says "SLI Ready" on it. Here is the part number I ordered twice:
 
http://www.ocztechnology....ition_4gb_dual_channel
 
I ordered one kit in 2009 and a second kit (same part number) in 2010. The packaging is slightly different in both kits and the modules themselves also look slightly different. Because of this discrepancy, I installed the 2009 kit in slots 0 and 1 (gray color slots). The 2010 kit is installed in slots 2 and 3 (black color slots ).
 
So you guys think that SLI-Ready gets set to disabled no matter what when installing 4 sticks on the 780i board? This shouldn't affect performance right?
 
 
Here are some Pics of my BIOS:
 
MEMORY CONFIG

 
MEMORY TIMINGS

 
VOLTAGES

Manufacturer recommends 5-4-4-15. Mine are running a bit faster. Wouldn't it be better to leave them as is?

Here are the questions I ask Patriot and their response back to me.
 

 
My next step is to find out if there is something wrong with my system since memory is maxed and EPP 2.0 is detected and seemingly working fine, I haven't seen an error yet and it been a couple of  months. 
 
EDIT: The answers to my next question are below.

Hope this help clarify this for everyone. After I get some info from Nvidia we should be done with this subject.
EDIT: I am not running memory at 2000MHz speed on my mother board. When I stated that things seemd to be working fine with EPP 2.0 settings it was because all of the settings changed properly in BIOS when EPP was enabled however those settings were never left that way on my system. Instead I am running my SLI detected memory in EXPERT mode, linked and sync'd (1333MHz).

JeffreyHam

So, my earlier statement seems to still stand true.......For most folks, the EPP/SLI Feature will get disabled when 4 stix are installed into the MoBo.

Jeffrey, I never felt you were wrong. If you have a second go back and re-read my post to you. You actually opened my eyes on this more than before and I went back to edit my response to reflect that eye opening not long after initially posting.
 
This has been a good debate and as Napathanes pointed out it looks like we are both right. Based solely on volume of affceted users it appears you are more right than I. I also think trying to get an answer which is more specific, why some see SLI detected memory and others do not, will help everyone who has questions moving forward.
 
Personally it would be nice to find out if I got LUCKY and purchased some very compatible memory kits or if I am having an abnormal system issue.
 
When this thread began I had no idea so many users were experiencing full memory complements of memory not being detected as SLI ready. I did know of some who had the non-detection issue with memory of different specs while I also knew all 4 sticks (8GB) of my memory and a few other users memory is detected as SLI memory. Based on what I had seen this led me to believe it has to do with compatibility of memory kits when combined on the same motherboard. I still believe that but with the exception Patriot pointed out "EPP could not be enabled on earlier revisions of 790I boards". Patriot did go on to say "it may be different now".
 
The question remaining is why some memory beyond two sticks is detected as SLI memory? I believe we have  a large part of the answer to that question provided to us by Patriot in the dialogue with them. The part we do not have is a statement from Nvidia, who are the basic designers of the SLI Ready memory function who can add insight to the evolution of our mother boards and EPP memory.
 
I am under the impression companies like EVGA, MSI, ASUS, and others who make quality and discrete functionality modifications to the basic Nvidia design do so by changing the quality, type of circuit components (Caps, resistors, diodes, and so on), and minor dircuit changes leaving the functionality of the basic Nvidia design concept unchanged. The quality and type of changes opens up our mother boards to enhanced performance and abilities beyond Nvidias basic design. It is possible some of these manufacturing changes may play a role in how and when memory is detected as I believe Patriot was pointing out.
 
Like mother board manufacturers change things memory manufacturers also may make changes to memory sticks in much the same way. This could also affect who sees memory detected as SLI ready. All of the combinations or revisions, products, and designs could yeald infinite conclusions.
 
A statement from Nvidia will likely not close the information hole on this issue completely (mother board and memory manufacturers would all need looked at independently and togather)  but it may provide enough information to make this more easily understood. Nvidia is the only source of information who can speak to mother boards and memory as a designer.
 

duntlessManufacturer recommends 5-4-4-15. Mine are running a bit faster. Wouldn't it be better to leave them as is?

My statement to thread OP would be take the advice of others here and do not be concerned if your memory is not detected as SLI memory. Set your memory settings manually and if you run into questions and need help let the members here work with you. As for your timings and which are better I cannot answer for Napathanes but I can give you my thoughts. Napathane likely said set timings to manufacturer recomendations because when adding additional RAM over 2 sticks many times timings have to be loosened to insure continued reliability and operation. I am presently running my memory more tightly but I am not planning on leaving things this way very long, I only took that option because of curiosity, I am running my memory 66% of rated speed and everything passed testing. When I over clock my system memory timings will certainly change likely to manufacturer specs as it approaces 80% of speed ratings. You and I also need to consider our memory controler and lane busses ability to handle the increased stress of 4 sticks as Patriot pointed out to me.

We could spend the rest of our lives trying to figure out why SLI gets disabled for some and not for others when installing 4 stix. I personally, think it is a waste of time worrying about it as, it really makes no difference to how well the RAM functions if it enabled or not.
 
EDIT: My model of RAM has the Intel XMP Profiles (Intel's version of the SLI/EPP Profiles) and my board cannot read/detect these profiles to be able to use them. However, CPU-z CAN read them and display them to me so that I know what they are. I am running on one of them as my everyday settings (see my CPU-z Validation Link)....I just had to manually set it into the BIOS.
 
Here is what they are (plus, there are also JEDEC Standard Timings at 914MHz and 1066MHz for BIOS Safe Mode booting):
 

XMP timings table  CL-tRCD-tRP-tRAS-tRC-CR @ frequency (voltage)
                XMP #1   6.0-6-6-18-31-2T @ 685 MHz (1.900 Volts) = 1370MHz 
                XMP #2   7.0-7-7-20-36-2T @ 800 MHz (1.900 Volts) = 1600MHz
                XMP #3   8.0-8-8-23-47-2T @ 914 MHz (1.900 Volts) = 1828MHz **what I'm running**
                XMP #4   9.0-9-9-26-47-2T @ 1028 MHz (1.900 Volts) = 2056MHz
                XMP #5   10.0-10-10-29-52-2T @ 1142 MHz (1.900 Volts) = 2284MHz

Looks like you may have not gotten all the possible info. Open CPU-z, click on the About Tab and at the bottom in the Tools Section, click on the Save Report (.txt) button. Save the report to the location of your choice (I save to Desktop) and go thru it. You may then find a more detailed EPP timings table....I do not know so,....please let me know what ya get.