You gentlemen were right as usual.  I replaced the DVI cable with a 
DPORT->HDMI and now have all 3 monitors working on my development 
workstation.

Now my only problem is how to fit 4 monitors on my desk and decide if I 
need a 3rd HDMI switch.

Life is good.

Thanks again!

Best,
Joe

On 04/14/2015 08:37 AM, Joseph Areeda wrote:
> Thank you Konstantin and Mark,
>
> I am using the nVidia driver not the one in the repo although I have 
> tried both.
>
> The monitors all run at 1920x1080 with hdmi input but they use the 
> hdmi, dport and dvi outputs of the card.  Just because of the cables I 
> had on hand.
>
> I think the next thing to try is to replace the DVI->HDMI cable with a 
> DPORT->HDMI cable (this card has 4 DPORT, 1 HDMI, 1 DVI).
>
> I would think both of your experience suggest no software issues.
>
> Thanks again!
>
> Joe
>
>
> On 04/13/2015 12:48 PM, Konstantin Olchanski wrote:
>> On Wed, Apr 08, 2015 at 09:21:17PM -0700, Joseph Areeda wrote:
>>> So I bought a new GTX960 which purports to support 4 monitors so I
>>> hooked up a third one but SL6 still only sees 2.
>>>
>>
>> In my experience, requirements for multi-monitor support are poorly
>> documented for most video cards.
>>
>> For example, the ASUS Z87/Z97 mobo has 3 video outputs connected
>> to the on-CPU video. It is supposed to support 3 monitors,
>> but to actually make it work, I had to get down all the way to
>> data sheet for the on-CPU video controller where they explain
>> how due to a missing clock (3 clock sources needed, only 2 available),
>> all 3 monitors have to run at identical resolution and that
>> only some combinations of DVI and DisplayPort connections
>> are supported (3 DVI is okey, 2 DVI + 1 DP not okey, or some such
>> arcane rules).
>>
>> In practice, it means that all 3 monitors have to be identical,
>> all connected with DVI-to-{HDMI,DP,miniDP} cables (passive adapters).
>>
>> Maybe you have mismatched monitors and your particular combination
>> cannot be done by the hardware (and good luck finding the nvidia
>> documentation for this - intel seems to do better with public docs).
>>
>> Again, in practice, if you have nvidia video card, install latest 
>> kmod-nvidia (from elrepo
>> or otherwise), run "nvidia-settings" and your monitors do not show up,
>> you are toast.
>>
>> (Some vendors are upfront with these problems - ASUS AMD socket AM1 mobo
>> plainly states - 3 video outputs - VGA, DVI, HDMI - but only 2 monitors
>> can be connected).
>>
>>
>> K.O.
>>
>>
>>> I still have some debugery to do but I wanted to ask if anyone has
>>> gotten more than 2 monitors to work on one video card?
>>>
>>> That will help direct my efforts.
>>>
>>> For the record the output of nvidia-smi looks like:
>>>
>>>     +------------------------------------------------------+
>>>     | NVIDIA-SMI 346.59     Driver Version: 346.59 |
>>> |-------------------------------+----------------------+----------------------+
>>>     | GPU  Name        Persistence-M| Bus-Id        Disp.A | Volatile
>>>     Uncorr. ECC |
>>>     | Fan  Temp  Perf  Pwr:Usage/Cap|         Memory-Usage | GPU-Util
>>> Compute M. |
>>> |===============================+======================+======================|
>>>     |   0  GeForce GTX 960     Off  | 0000:01:00.0     N/A
>>>     |                  N/A |
>>>     |  0%   46C    P8    N/A /  N/A |    370MiB /  2047MiB | N/A
>>> Default |
>>> +-------------------------------+----------------------+----------------------+
>>>
>>> +-----------------------------------------------------------------------------+
>>>     | Processes: GPU Memory |
>>>     |  GPU       PID  Type  Process name
>>> Usage      |
>>> |=============================================================================|
>>>     |    0            C+G   Not
>>>     Supported                                         |
>>> +-----------------------------------------------------------------------------+
>>>
>>>
>>> thanks,
>>> Joe
>>>