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View Full Version : 7800GT core clock comparison - this is messed up.


fuelrod
09-13-05, 09:11 PM
I’ll try to keep this as short as possible, here it goes ….

If you have heard or seen the digit-life article (http://www.digit-life.com/articles2/video/g70-2.html) then you know the 7800 series has three separate core clocks, Geometric (geo), Shader (shd), and ROP. As you will see different venders are using different methods of driving these clocks and I wanted to share what I have found out.

I started down this path when I got my EVGA 7800GT and got what I thought was a poor overclock in relation to what I had been seeing on the net. The best I could get was 460 on the core. After RivaTuner came out with their latest version I was able to monitor the clocks and see what was happening. In the display panel my core was set to 445 default. When I started a 3D app, the geo core jumped to 486 (~40 points over default) while the shd and ROP were at 432. As I increased the display panel core the geo core would roughly track the display panel but the shd & ROP core would jump in increments at 432, 459, and 486. The jumps occurred between 445-446, 472-473 on the display panel core. I thought this was normal for all 7800 cards until ……

I flashed my card to the XFX 7800 bios (on a side note I was sweating big time because my wife would have killed me :fu: if I borked my new $400 card). With the XFX bios the default on the core is 450. Using RivaTuner I was shocked when I ran a 3D app the all three core were the same. As I increased the core, all three clocks (geo, shd, ROP) tracked with the display panel. Now it made since why I was seeing some people get 480-490 on their cores. The XFX doesn’t add the 40 point jump to the display panel core like the EVGA card.

“What did this do for my overclock?”, glad you asked. With the EVGA bios I could get 460 which translated to 500-geo, 459-shd, and 459-ROP. With the XFX bios I could get 474 which translated to 474-geo, 474-shd, and 474-ROP. My theory as to why the XFX bios topped out at 474 is that even though my geo part of the core could go higher (as proved by the EVGA bios) the shd and ROP parts of the core couldn’t take anything higher than 474.

Conclusion

Different venders are using different methods of driving the 7800 series core clocks and it’s going to make comparing possible overclocks of these cards next to impossible. In my case, I get better benchmark scores with the EVGA bios at 460 in the display panel than with the XFX bios at 474 in the display panel. I assume this is because my +26 point difference in the geo core makes up for the -15 point difference in the shd and ROP cores. In the end I went back to my original EVGA bios; 460 EVGA beats 474 XFX, go figure. Hopefully someone will find this useful. Maybe someone with some more time could test other bios. I promise only the first bios flash scares the crap out of you. :thumbsup:

balex99
09-14-05, 09:23 PM
Well from what I have been reading on the forums, I just hope mine works at the default clocks. I have seen some that are getting artifacts at default clocks and have had to resort to bringing the core clock down to 425 which would essentially be 465 by your numbers.

I'll find out tomorrow. I am sitting here at work with my new Evga 7800GT and Evga SLI board. It is going to be a long 7 hours.

-=DVS=-
09-15-05, 01:04 AM
This is my max OC with BFG card i wonder what kind of results i could get with XFX bios , a bit scared to flash video bios :( , you did it from DOS "fuelrod" , just like Motherboard ?
http://img345.imageshack.us/img345/627/5005to.jpg

Peoples-Agent
09-15-05, 02:31 AM
Strange stuff, so the overclocking on these things is alot different then....sheesh.

I got my Gigabyte 7800 sat here, awaiting some more parts today including a nice hefty power supply with the vision of overclocking this baby like I did with my previous 6800GT but its sounding alot more complicated than previous generations.

Good post there Fuelrod, really is some food for thought.

mrgimble
09-15-05, 07:25 AM
So how did the different BIOS and overclocking affect performance? Did you do any benchmarking before and after to see if it made any real differnce?

fuelrod
09-15-05, 10:52 AM
This is my max OC with BFG card i wonder what kind of results i could get with XFX bios , a bit scared to flash video bios :( , you did it from DOS "fuelrod" , just like Motherboard ?

Yes I did it from a boot floppy using nvFlash 5.13 from here http://www.mvktech.net/index.php?option=com_remository&Itemid=26&func=selectfolder&filecatid=42

Just follow this guide http://www.mvktech.net/content/view/15/37/

That site has several 7800GT bios as well. If you look at all the bios revs they are very similar (EX. EVGA is 5.70.02.13.01, BFG is 5.70.02.13.07, XFX is 5.70.02.13.12) I don't think there is much difference between them except for a vender ID and how they drive the core clocks. It is scary the first time but I don't think you will have a problem.


So how did the different BIOS and overclocking affect performance? Did you do any benchmarking before and after to see if it made any real differnce?

Yes I did some bench marking using 3Dmak 05. In the overall score it was higher with the EVGA bios at 460 overclock compared to the XFX at 474 overclock by 2-3%. Like I said before I think this is because at 460 the EVGA geo core is at 500 whereas at 474 the XFX core is at 474. But it was interesting the shader specific test was 4% higher on the XFX bios compared to the EVGA. I think this was because at 474 the XFX shd & ROP cores are at 474 whereas at 460 the EVGA shd & ROP cores are at 459.

So to make a long story short I think different applications will benchmark differently based on how geo core intense the application is vs shd & ROP core intense. nVidia has put out a good product but they have made it extremely hard to compare cards across different applications.

Mr_LoL
09-15-05, 11:18 AM
Does this mean that with an xfx bios, you could get a bigger overclock?

fuelrod
09-15-05, 01:48 PM
Does this mean that with an xfx bios, you could get a bigger overclock?

It could mean that if the geo part of the core is what is holding you back. With EVGA, for whatever reason, they add 40 Hz to the geo core when a 3D app is started. In my case this allows my geo core to get to 500 while my shd & ROP core are locked at 459. With the XFX bios, if I was not limited by the shd & ROP cores (474 for me) I could technically go to 500 on all three cores which would be a much better overclock. It really just depends on which part of the core is holding you back.

J-Mag
09-15-05, 03:10 PM
FYI, you must disable fake ddr workaround to report proper speeds on the 7 series cards, with Riva Tuner

Fake DDR workaround algorithm is forced by default in 15.7 for GeForce 7800 series. To get effective memory clock readings on these chips you'll need to disable it manually:

PowerUser -> Open RivaTuner.rtd -> RivaTuner ... \Overclocking\NVIDIA -> FakeDDRWorkaround -> 0

Although I don't think this has anything to do with core clocks...

XFX BIOSes for 7 series have same low power 3d and full 3d speeds too, none of the other BIOSes I have seen do that.


One more thing: Anyone try a negative value for ROP or GEO clock increase with Nibitor?