The SLI option on the NVIDIA Control Panel doesn't show up for my two EVGA GTX 660s.

[bazeroni]

Both are connected by an ASUS flexible SLI bridge and are correctly installed into both GPU slots on my HP xw6600 Workstation Base Unit's motherboard.

 

[Sergeant_Sneaky]

Does the motherboard actually support SLI? What motherboard is it?

 

[Rogue Leader]

That HP Intel XW series machines do not support SLI or Crossfire. As do most workstation based systems. No way around this, sorry.

 

[SoNic67]

Workstations are not listed for SLI or Crossfire, there is no purpose for that in professional world and there is a licensing cost associated with those technologies.
However you can try the software called "DifferentSLIAuto NVIDIA Driver Patcher and Signer", it worked on a Dell T3500 Workstation.
https://github.com/EmberVulpix/DifferentSLIAuto/releases

 

[bazeroni]

Does the motherboard actually support SLI? What motherboard is it?

the previous owner of the pc ran two gt 9500s SLI on windows 7. he then upgraded to windows 10 which is what im trying to run it on now

 

[bazeroni]

Does the motherboard actually support SLI? What motherboard is it?

'
the link you gave me didn't change the settings in my NVIDIA Control Panel if that was the purpose of it. I got a windows update though when i rebooted. If I would need a different motherboard what would you recommend?