Installation of any of the AMD Radeon cards is really easy. Once the card is seated into the PC, make sure you hook up the monitor and of course any external power connectors like 6 and/or 8-pin PEG power connectors. Preferably get yourself a power supply that has these PCIe PEG connectors native (converting them from a Molex Peripheral connector anno 2013 we feel is a no-go).
Once done, we boot into Windows, install the latest ATI Catalyst drivers and after a reboot all should be working.
Mind you though that in the Catalyst Control panel you'll need to activate Crossfire mode manually if you are using two cards. No further configuration is required or needed unless you like to tweak the settings, for which you can open the Catalyst Control Center.
Let's have a look at how much power draw we measure with this graphics card installed. The methodology: We have a device constantly monitoring the power draw from the PC. We simply stress the GPU, not the processor. The before and after wattage will tell us roughly how much power a graphics card is consuming under load. Our test system is based on a power hungry Core i7 - X79 system. This setup is overclocked to 4.60 GHz on all cores. Next to that we have energy saving functions disabled for this motherboard and processor (to ensure consistent benchmark results). On average we are using roughly 50 to 100 Watts more than a standard PC due to higher CPU clock settings, water-cooling, additional cold cathode lights etc. We'll be calculating the GPU power consumption here, not the total PC power consumption.
Measured power consumption - single card
System in IDLE = 119W
System Wattage with GPU in FULL Stress = 498W
Difference (GPU load) = 379W
Add average IDLE GPU wattage ~10W
Subjective obtained GPU power consumption = ~ 389 Watts
Mind you that the system wattage is measured at the wall socket side and there are other variables like PSU power efficiency. So this is a calculated value, albeit a very good one.
Above, a chart of relative power consumption. Again the Wattage shown is the card with the GPU(s) stressed 100%, showing only the peak GPU power draw, not the power consumption of the entire PC and not the average gaming power consumption.
Here is Guru3D's power supply recommendation:
Radeon HD 7990 - On your average system the card requires you to have a 750 Watt power supply unit.
Radeon HD 7990 Crossfire - On your average system the cards require you to have a 1000 Watt power supply unit as minimum.
If you are going to overclock GPU or processor, then we do recommend you purchase something with some more stamina.
There are many good PSUs out there, please do have a look at our many PSU reviews as we have loads of recommended PSUs for you to check out in there. What would happen if your PSU can't cope with the load.
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