Overclocking the 7800 GTX

To get an indication of how well the GeForce 7800 GTX scales, we decided to overclock our reference boards sent to us by NVIDIA, as well as EVGA’s e-GeForce 7800 GTX card. EVGA’s board differs slightly from the NVIDIA reference board, with a core clock speed of 450MHz, 20MHz higher than the stock 7800 GTX speed of 430MHz. The memory speed remains the same as the 7800 GTX reference board, at 600MHz.

Other graphics manufacturers are doing this with their 7800 GTX boards as well, suggesting that the chip could have a little bit of headroom for overclocking...

How to overclock your GeForce 7800 GTX

For years, NVIDIA’s Coolbits registry modification has been our favorite method of overclocking GeForce cards. NVIDIA has quietly provided this technique to any NVIDIA card owner in their driver, although it’s officially unsupported.

Add Coolbits DWORD value here

Set it to 3

To overclock your board, simply open the Windows Registry Editor by typing "regedit" in the Run Menu of Windows. Then open the following directory:
"HKEY_LOCAL_MACHINE\\Software\\NVIDIA Corporation\\Global\\NVTweak". Next, right-click on the NVTweak key and create a new dword value named "Coolbits." Adjust the value of Coolbits to "3" by double clicking on it and entering "3" in the value data field. Once you’re done, restart Windows to apply your new settings.

After a quick Windows restart, you’ll now see a new field in your driver’s control panel titled “Clock Frequency Settings”, this is where you’ll overclock your 7800 GTX card (or any other NVIDIA card for that matter). Select “Manual overclocking” if you’d like to adjust the graphics core and memory speeds yourself, or “Auto overclocking” if you’d like the graphics driver to determine the highest speeds based on temperature (ala ATI OVERDRIVE. In SLI mode, the manual overclocking mode is your only option available.



So how far were we able to overclock our GeForce 7800 GTX boards? Pretty far actually. Our best overclock was achieved by one of the NVIDIA reference boards, which hit 505MHz core/670MHz memory (1.34GHz effective).

This is an improvement of 15% on the graphics core, and 10% on the memory.

The second reference card topped out at 489MHz core/658MHz memory, still not bad at all in our opinion. Our EVGA card also maxed out at 489MHz core, with the memory hitting 638MHz.

After reboot, you'll see this added to the NVIDIA control panel

By default, the 7800 GTX runs at 275MHz core in 2D mode

EVGA 7800 GTX stock clocks

Of course, we couldn’t stop at just testing a single-card GeForce 7800 GTX configuration, we were also curious to see how two overclocked 7800 GTX boards fared when running in SLI. The highest clock speeds we could attain without artifacts and complete stability was 476MHz core/640MHz memory. This was achieved using the two NVIDIA reference boards (in all honesty, the EVGA is built on the same reference board design, only it ships with higher stock clocks).

The clock speeds are a little bit lower because the temps of the SLI configuration are higher. The master 7800 GTX board located in the first PCI Express slot will always operate hotter than the slave card below it, as the card’s fan is obstructed by the slave board, cutting off its air supply. In NVIDIA’s upcoming ForceWare 80 series driver, end user’s will be able to overclock the master and slave cards independently of each other, which will allow you to run your slave board a little bit faster than the master board for better performance.