NVIDIA GeForce 6800 GT and GeForce 6800: Overclocking and Modding

Today we are going to take a closer look at the two latest graphics solutions from NVIDIA based on GeForce 6800 and GeForce 6800 GT working at their nominal frequency and at overclocked frequencies after a few sophisticated modifications of ours. Find out now what you can get for your buck!

by Tim Tscheblockov
07/26/2004 | 01:00 PM

Within each new generation of graphics processors (or “half-generation” if we deal with a modification of the existing chip architecture) the leaders of the gaming 3D graphics, ATI Technologies and NVIDIA Corporation, put the fastest product in the spotlight. Such GPUs are the first to come to the hardware test labs, the first to get some reviews and praises, the first to confirm the technological superiority over the competitor.


Today, ATI and NVIDIA are offering the RADEON X800 and the GeForce 6 series, respectively as their most advanced products, among which the RADEON X800 XT Platinum Edition and NVIDIA GeForce 6800 Ultra chips are the fastest. Of course, the price of the newcomers is rather steep – about the same money as you would pay for a mainstream system case with all the stuffing!

This is not a reason to spend your last money, though. Top-end products are always followed by less expensive ones, and they are of a great interest to overclockers: these graphics cards are based on the same GPUs as the top-end products, but work at reduced frequencies and have fewer enabled pipelines, and that means there’re a lot of opportunities to overclock and experiment and turn those disabled pipelines back on!

NVIDIA’s series of products with the GeForce 6 architecture seems rather more interesting so far: besides the front-liner GeForce 6800 Ultra, it includes two less expensive solutions:

ATI’s now supplying only the top-end RADEON X800 XT Platinum Edition and, as a less expensive variant, the “cut-down” RADEON X800 Pro with 12 pixel pipelines. NVIDIA’s selection gives you more flexibility: you can choose between the “cut-down” GeForce 6800 with 12 pixel pipelines and the full-featured GeForce 6800 GT that only has lower frequencies compared to the GeForce 6800 Ultra.

Now, let’s see what the GeForce 6800 GT and GeForce 6800 are capable of at the standard as well as overclocked frequencies.

NVIDIA GeForce 6800 GT

The GeForce 6800 GT is a cheapened GeForce 6800 Ultra with slightly smaller GPU and memory frequencies. The GT has the same number of pipelines as the Ultra, i.e. the GeForce 6800 GT carries a normal NV40 processor on board.

We’ve got a reference GeForce 6800 GT card from NVIDIA:

You may note that the GeForce 6800 GT is made by the same design guidelines as the GeForce 6800 Ultra.

However, the GT works at reduced clock rates and consumes less power, so there’s only one power connector on the card:

The cooling system is rather average by today’s standards. It consists of two aluminum heatsinks that cover the core and the graphics memory chips:

Thermal compound lies on the graphics core, and thick heat-conductive pads are the thermal interface to the memory chips.

A fan is fastened above the heatsinks – a thin aluminum plate directs the air stream along their ribs:

Again, the card is based on the NVIDIA GeForce 6800 GT graphics processor (NV40 core) that is normally clocked at 350MHz:

Like the GeForce 6800 Ultra, the GT model has 256MB of GDDR3 memory, but its frequency is reduced to 1000MHz. The reference card uses 2ns GDDR3 chips from Samsung:

The card did well at overclocking: the maximum stable frequencies were 420MHz GPU and 1150MHz memory. That’s really a nice performance bonus – the card exceeded the clock rates of the GeForce 6800 Ultra!

I reached those clock rates using the standard cooling system and without any other tricks. Let’s now check the card with a water-cooling system by installing the Aquarius II from Thermaltake:

The stable frequencies are 450/1150MHz now.

The GPU frequency only grew up by 30MHz: this 420-450MHz range may be the overclockability peak for this particular sample of the NV40 without voltage adjustments or extreme cooling solutions. Anyway, those 450 megahertz – 28.5% above the nominal frequency – are good by themselves.

The maximum frequency of the graphics memory didn’t change with the installation of the water-cooling system on the GPU – that’s natural. 1150MHz is not too much for graphics memory chips that are normally clocked at 1000MHz. However, we deal with GDDR3 here, and this memory remains a kind of stranger – we haven’t yet explored its potential fully. Maybe those 1150MHz (or 15% above the nominal frequency) are a good result after all.

So, the frequencies of the GeForce 6800 GT easily exceeded the regular clock rates of the GeForce 6800 Ultra at overclocking.

NVIDIA GeForce 6800

The performance of the GeForce 6800 has been cut down severely, even in comparison to the GT version: it only has 12 pixel pipelines and works at still lower frequencies.

As an example of a GeForce 6800-based card I took the WinFast A400 TDH model from Leadtek:

Our test lab received the retail version of this graphics card:

The GeForce 6800 consumes less power than even the GeForce 6800 GT, having fewer pipelines and lower frequencies, so this card is equipped with only one connector for supplying additional power:

Although having smaller power dissipation than the GT model, the Leadtek card boasts a more serious cooling system:

The face-side cooler with a copper heatsink takes heat off the graphics core and the memory chips. The backside of the PCB is covered under a massive copper heat-spreader.

The wiring layout of the GeForce 6800 differs from the reference design of GeForce 6800 Ultra/GT cards, but the presence of a mighty-looking heat-spreader on the back side of the PCB doesn’t mean that there are any memory chips there. This heat-spreader removes heat from under the memory chips. Thick and soft thermal pads serve as a thermal interface there.

The Leadtek WinFast A400 TDH features the NVIDIA GeForce 6800 GPU that works at a frequency of 325MHz.

This graphics card is equipped with 128MB of ordinary DDR SDRAM in 2.8ns chips from Hynix that work at 700MHz:

The NVIDIA GeForce 6800 is a simpler chip compared to the GeForce 6800/6800GT – it has some of its pixel pipelines turned off. The reduced power consumption and heat dissipation of the GeForce 6800 game me some hope that this processor would have a high overclockability. Contrary to my expectations, this sample was rather unwilling to increase the core frequency: the maximum frequencies at which the card was stable were 390/950MHz. That is, the core frequency grew by 20% exactly and the memory frequency grew more, by 36%. In order to install a water-cooling system without leaving the memory chips bare, I just took the memory heatsink from the GeForce 6800 GT reference card and put it on Leadtek’s GeForce 6800: the two cards have different wiring, but the holes for fastening the cooling system are identical in them.

After my installing the water-cooling system, the maximum stable frequencies of the card were 400/975MHz (+23% GPU frequency and +39% memory frequency).

Before getting to the tests, I can’t help expressing my thoughts on the subject that worries every good overclocker with respect to the GeForce 6800. So, the question sounds like this: Is it possible to turn on all of the 16 pipelines on the NVIDIA GeForce 6800?

Yes, it is! This is easy: just flash the BIOS from the GeForce 6800 Ultra. After the BIOS re-flash, the graphics processor enables all 16 pixel pipelines and the card becomes… NON-OPERATIONAL!

Why? Because those four missing pipelines hadn’t been disabled just for nothing – they have certain defects, which show themselves as artifacts in 3D applications after you enable those pipelines. You won’t have the opportunity of returning things back easily: after flashing back the BIOS from the 12-pipelined GeForce 6800 you’ll see that the situation remains the same – the card still has 16 pipelines and also has those 3D artifacts. In order to disable the defective pipe-work and restore the card’s operability you will need special software and a specially modified version of the BIOS.

Thus, although it is possible to transform a GeForce 6800 into a GeForce 6800 Ultra/GT by turning on all 16 pipelines, there’s no practical gain from that so far: the disabled pipelines are 100% sure to have defects and their turning on results in various visual artifacts.

There’s no sense to hope that some of NVIDIA’s GeForce 6800 chips have 16 “healthy” pipelines and some of them are just disabled for no particular reason – NVIDIA is not in a position to make such gifts today. The chips are tested back at the factory and are immediately sorted. Fully operational chips are transformed into the GeForce 6800 Ultra/GT, and those that have certain defects – defects that that can be avoided by disabling a few pipelines – become the 12-pipelined GeForce 6800.

It is of course possible that the NV40 manufacturing process will be improved after a while. In this case, there will be an insufficient amount of defective chips to produce the GeForce 6800 in mass quantities, and NVIDIA will have to turn pipelines off in fully operational chips. By that time, however, NVIDIA will certainly have introduced various protection techniques, and it will be less easy to make any kind of conversion to the GeForce 6800.

Testbed and Methods

The testbed was configured as follows:


ATI’s Catalyst driver enables optimizations of tri-linear and anisotropic filtering even at the maximum quality settings and you cannot turn them off from the driver’s control panel. So, to create similar environments for all the test participants, I selected the maximum quality mode for the graphics cards on ATI’s chips and the “Quality” mode with enabled tri-linear and anisotropic filtering optimizations for cards on NVIDIA’s GPUs.

The internal settings of each game were set up for the maximum possible image quality. There are two test modes: “pure speed” and “eye candy”, the latter uses 4x full-screen anti-aliasing and 16x anisotropic filtering (8x anisotropy level for the NVIDIA GeForce FX 5950 Ultra).

Performance in Gaming Applications

Far Cry

NVIDIA’s GeForce 6800 GT lags behind the GeForce 6800 Ultra and ATI’s RADEON X800 XT in Far Cry, but surpasses the cheaper version of the X800, the RADEON X800 Pro. The overclocked GeForce 6800 GT is faster than the 6800 Ultra as well as the X800 XT and becomes the leader. The slowest version of the NV40, the GeForce 6800, cannot compete with the 6800 GT or the X800 Pro even when overclocked, but it easily leaves behind the top-end products of the last generation, the GeForce FX 5950 Ultra and the RADEON 9800 XT.

The GeForce 6800 GT remains ahead of the RADEON X800 Pro in the “eye candy” mode with enabled full-screen anti-aliasing and anisotropic filtering. At the overclocked frequencies, it is superior to the GeForce 6800 Ultra, too, but loses to the RADEON X800 XT, which is most efficient in this hard operational mode.

Having only 12 pixel pipelines, reduced frequencies and a smaller amount of the graphics memory, the GeForce 6800 falls behind the leaders more in higher resolutions – in 1600x1200 it even loses to the RADEON 9800 XT and the GeForce FX 5950 Ultra! Overclocking only helps it outperform the GeForce 5950 Ultra in the hardest mode, but the RADEON 9800 XT remains unreachable.

Probably, the 12-pipelined GeForce 6800 chip, like the RADEON X800 Pro, has a less efficient realization of the hidden surface removal technique compared to the chips with 16 pipelines, and it becomes another performance-reducing factor, especially in “hard” modes with full-screen anti-aliasing.

Prince of Persia: Sands of Time

The GeForce 6800 GT is on the level of the RADEON X800 XT in Prince of Persia, losing to the GeForce 6800 Ultra. At overclocking, it surpasses the Ultra version of the NV40, too.

At its regular frequencies, the GeForce 6800 is slightly better than the RADEON X800 Pro, but reaches the level of the 16-pipelined NVIDIA GeForce 6800 GT at overclocking.

That’s an interesting result, don’t you agree? Even overclocked, the 12-pipelined GeForce 6800 has a smaller fill rate in comparison to the GeForce 6800 GT, so it evidently owns its advantage to something else. For example, it may have a better vertex performance – the 6800 has the same number of vertex pipelines as the GeForce 6800 Ultra/GT have – or faster internal caches.

Max Payne 2

The results in high resolutions are less limited by the CPU performance, and the GeForce 6800 cannot compete with the GeForce 6800 GT or the RADEON X800 Pro even at overclocking.

The results of the GeForce 6800 GT, like those of the GeForce 6800 Ultra and RADEON X800 XT/Pro, are limited by the CPU speed even in the highest resolutions.

On enabling full-screen anti-aliasing and anisotropic filtering, we see the results of the fastest cards limited by the CPU speed up to the 1280x1024 resolution. The NVIDIA GeForce 6800 GT is just a little worse than the GeForce 6800 Ultra and the RADEON XT/Pro. The GeForce 6800 loses its ground in the hardest modes and sinks below the level of the RADEON 9800 XT.


Before making any final comments, I think it right to quote the prices NVIDIA and ATI recommend for their products. Of course, these are only recommendations and we know that the real level of the prices is usually determined by the market situation. After announcements and in view of a product deficit the prices may skyrocket up in no time. Anyway:

Well, the GeForce 6800 GT certainly looks more appealing with such pricing than its rival, the RADEON X800 Pro. First, even without overclocking, the GT is overall faster than the X800 Pro. Second, GeForce 6800 GT graphics cards, unlike RADEON X800 Pro-based ones, carry a healthy 16-pipelined chip, which can easily overclock to the frequencies (and, as our tests suggest, the performance!) of the top-end GeForce 6800 Ultra model and more. The weakest NV40-based model, the GeForce 6800 with 12 pipelines doesn’t face an immediate rival from ATI yet, since the 12-pipelined X800 Pro is above the GeForce 6800, in terms of both price and performance.

The conversion of the GeForce 6800 into a “full-fledged” chip, i.e. turning on its all 16 pipelines, does work, but to no practical effect: the disabled pipelines are really defective. The most unpleasant fact is that the conversion procedure is not revocable in home conditions: you can flash a BIOS from the full-featured card and get the visual artifacts in games, but you cannot bring the card back to the norm by simply flashing the old BIOS back.

The impression about the GeForce 6800 is also spoiled somewhat by the serious performance hit it suffers in the hardest display modes with full-screen anti-aliasing and anisotropic filtering enabled. In such situations, the GeForce 6800 may even lose to the top-end GPUs of the previous generation, i.e. to the GeForce 5950 Ultra and the RADEON 9800XT. But overall, this card seems to be an excellent alternative to graphics cards based on these two chips – the GeForce 6800 leaves them far behind in simpler modes. If GeForce 6800 graphics cards do start selling for about $300, products on the RADEON 9800 XT and the GeForce 5950 Ultra will have no chance in the market, considering their current pricing.

So, we’re waiting for the graphics cards to appear in shops in mass quantities!