To run three monitors you will need at least a GT 640 or higher, and to run four monitors you need a GTX 650Ti Boost or higher. In the 700 series, all cards support three monitors, and the GTX 760 or higher supporst four monitors.

For any other Nvidia cards you will need two Nvidia cards. One of the two cards needs to have dual video outputs.* To run 4 monitors both cards would need two video outputs. Add additional cards for each additional monitor. If you run out of PCI-E ports, or are using AGP, PCI cards can be used, althought multiple PCI cards may not function well together and issues may arise. Not all cards can be used in conjunction with one another. Be sure that drivers exist for and offer support for both cards. UV+ and other usb to VGA or USB to DVI adapters can also be used in liu of video cards.

*NOTE: VGA and S-Video cannot be used together. Cards with one VGA and one S-Video port do not have dual output.