Recently installed Mojave in my Mac pro 5.1 tower GPU is a GTX 460. I have several drives with earlier versions of OSX El Cap, Mavericks etc. According the many different things I have read you cannot have two video cards installed while running Mojave. Along with the GTX 640 I also have a GT120 in the tower which is not tethered to any monitor. When I boot into EL Capitan and later on boot to Mojave the dock vanishes along with all the icons for the internal drives. Selected View options does nothing as the drive options are checked off. The entire desk top appears darker and more pixelated. I found that rebooting and zapping the PRAM fixes theses issues until a boot into an earlier OS. Is this a viable work around zapping the PRAM every time I boot into Mojave or could this create more problems down the road. Needless to say I would like to keep the GT120 in the tower in case I need recover a drive etc.