GIGABYTE 3D1-68GT: Double fun
Specifications
For reference, we are bringing in the specifications for 3D1-68GT video card:
- Two GeForce 6800GT VPUs, operating frequency 375 MHz
- Total capacity of installed video memory - 512 MB, 16 chips in the BGA package, 8 per each side of the video card
- Two memory buses, each of 256 bit (each GPU uses its own 256 MB of memory)
- Memory type - DDR3, with 1.6 ns access time, operating frequency 1000 MHz
- Interface – PCI-E 16x
As you can see, the GPU frequencies are somehow overstated relative to the standard 350 MHz for 6800GT. It's hard to say what was the reason for such frequency overstatement. Perhaps the designed cooling system did such a good job that it was decided to raise the GPU operating frequency. Or, on the contrary, raise of frequency resulted in the need to develop such a massive cooling system. I presume the most probable reason was the manufacturer's wish to produce a result that would be much higher than the 20 000 marks threshold in 3DMark03. You might ask why 3DMark03 - it's now year 2005 which is coming to an end? We'll get the answer once we move to the tests. On the other hand, it is widely known that many video cards built on 6800GT easily overclock to frequencies equivalent to 6800Ultra. However, the "nominal overclocking" is a bit more modest. Among the natural limitations here is not much to do with the overclocking potentials of the GPU, but the increased total power consumption and heat emission of the video chip tandem.
The memory frequency fully meets the nominal for 6800GT even though the installed memory allows running at a higher frequency. On the whole, it us reasonable. Further raise of memory frequency does not produce such a radical effect upon the performance, but the above limitations for power consumption and heat emission play their part in here either.
However, despite all the reasoning behind the design and selected operation mode, it was not possible to avoid a fly in the ointment. As it turned out, the video card always runs at the same frequencies - both in the 3D and in the 2D modes. As you understand, such a behavior can't have a positive effect on the thermal mode of the video card and the system on the whole.
The second fly in the ointment is in that temperature monitoring is missing in 3D1-68GT. Neither RivaTuner, nor V-Tuner2 detected any temperature sensors, so showed nothing. Nor control for the coolers' rotational speeds was detected, which looks logical - the video card always heats up to the maximum.
It's hard to say what was the cause of mentioned flaws. Perhaps it is related to that engineers at Gigabyte had to write a special BIOS for 3D1-68GT, which resulted in some problems. Or, perhaps these are the tradeoffs for dual-chip nonstandard design. Or perhaps the lack of time. Anyway, that does not affect the stability of the video card. In any case, one will have to take care of a good ventilation of the housing and a powerful reliable PSU.
Overclocking
Prior to overclocking the video card manually, I decided to verify the automatic operation mode and "asked" the system to detect the optimum frequencies. The result surpassed my expectations. The drivers agreed that 375 MHz for the GPU is good albeit not enough and set 394 MHz, so decided not to touch the memory thus letting it merely 1030 MHz. Not bad. Recalling the overclocking capabilities of 6800 GT to the level of 6800 Ultra and the memory frequency margin, I certainly did not stop at that and decided to overclock 3D1-68GT a bit. In the end, the card showed a stable operation at 425/1200 MHz. As you can see, the frequencies meet the nominal frequencies for 6800 Ultra and even surpass them a bit (for the memory).
Benchmarking
Some preliminary notes (for those who don't like reading manuals). If we install 3D1-68GT into a motherboard that does not support SLI, the video card will run as a single 6800GT, but admit what's the point of having two GPUs then? So, to provide operation of 3D1-68GT video card in the maximum performance mode, a motherboard with support for SLI is a must! However, there are some fine points in here. Although support for SLI is a must, the switch changing the modes Normal/SLI has to be set to the Normal position. On the video card, the SW1 switch has to be set to the "ON" position (with the white dots turned to the bottom), as is seen on the Figure.
The switch itself is positioned on the rear side of the video card.
Attention! To change the SW1 switch to a different position, don't remove the radiator from the video card! The radiator won't close it.
Test-bench configuration:
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Test bench
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PCI-E
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CPU
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MB
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Memory
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OS
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WinXP + SP2 + DirectX 9.0c
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PSU
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For tests, we used NVIDIA's latest ForceWare 78.01 WHQL drivers.
3D1-68GT was tested in two modes. First - nominal frequencies 375/1000 MHz. Second - overclocked version, frequencies 425/1200 MHz (GPU/memory, respectively). The results were compared versus GeForce 7800GT, 7800GTX, and, since 3D1-68GT is essentially a couple of 6800GT in the SLI mode, we were curious to compare it against the top SLI-solution to date - 7800GTX-SLI.
Here are the results:
As expected, at the nominal frequencies 3D1-68GT takes a sure lead over 7800GT/GTX and approached the 10 000 marks "threshold". Overclocking helped to get over the 10 000 marks bar! Overclocked 3D1-68GT even surpasses 6800 Ultra-SLI perhaps due to a bit higher frequency of the video memory. Sure, 7800GTX-SLI remains inaccessible.
The alignment of forces is preserved. Note that 3D1-68GT demonstrates 20 327 "marks" at 3DMark'03 in the nominal mode. Can you see now why the box shows results just for 3DMark'03? At the nominal frequencies, 3D1-68GT fails to reach the 10 000 bar in 3DMark'05, while at 3DMark'03 it successfully demonstrates 20 000 "marks". The figure is more tempting! :) Going on.
Despite the two "heads" and overclocking, at this resolution the 3D1-68GT can't beat even the single 7800GT. To all appearances, the performance limitation of the CPU does not let 3D1-68GT show its worth. Let's see what will be at higher resolutions.
The assumption proved correct. 3D1-68GT showed results comparable to those for 7800GTX, while 7800GT shows a 10% lag.
Another increase in load upon the video subsystem is another proof of that 3D1-68GT is quite ready for that. While its predecessor 3D1 (one based on two 6600GT) was inferior to "single" 6xxx representatives in the most demanding modes, then 3D1-68GT competes on par in the Supreme League of today.
Low resolution and lack of CPU power smoothes out the difference in results. It seems like 3D1-68GT is very near to "beat" 7800GTX-SLI, but the miracle hasn't worked.
The difference becomes more noticeable. It is no longer possible to encroach upon the supremacy of 7800GTX-SLI, but rivals like 7800GT/GTX are not that close.
The picture does not change radically.
The most demanding game puts all dots on i's. Serious optimizations of video chips for the G70 generation were not lost on them. 3D1-68GT is desperately trying to stay on par. Only overclocking helps.
The situation is a bit better. 3D1-68GT is between two fires. 7800GT is pressing from beneath, and 7800GTX - from above.
The picture does not radically change, but there is one surprise. In the end, overclocked 3D1-68GT failed to pass the whole test throughout. In particular, it did pass it without artifacts, but regularly hung at the last frame of the test, thus we were unable to know the result. At the nominal frequencies, we found no problems. Nevertheless, I left the overclocked 3D1-68GT where it was. The result should be interpreted like this - "here could be the results for overclocked 3D1-68GT, if it were not for the unknown "bug" in the last frame which prevented us from seeing them".
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