How To Overclock Your Graphics Card

Introduction

Overclocking is more popular than ever. And since it’s so easy to boost the frequency of your Intel processor, it would be a shame not to. But CPUs aren’t the only components that can be overclocked. The GPUs on graphics cards can also be speeded up, and so can their memory. And since an affordable card only differs from more expensive ones in its clock speed, overclocking can be your key to some real savings.

Overclocking a GPU is a less common process than overclocking a CPU, and above all, it’s more complex. One of the reasons for that is that a graphics card’s BIOS is not as easily accessible as a motherboard’s. This article will shed some light on the different methods that can be used and the results you can expect when overclocking your graphics card.

Software or Hardware Overclocking?

It turns out that there are several ways to overclock your graphics card. We’ll take a look at each one in turn. First of all, you should know that you can overclock your card either temporarily, using Windows software utilities, or permanently by flashing your BIOS.

The Flexibility of Software

The first method is the best known. There are numerous utilities for AMD/ATI and Nvidia graphics cards. Their functions are often similar. The best ones let you set the operating speed of the GPU and the memory, but also the cooling power, and some let you load complete overclocking profiles and configurations of 3D functions to suit the application you’ll use. In fact, these utilities multiply the possibilities offered by the cards’ drivers. This implies that the ForceWare or Catalyst drivers are not totally ignorant of overclocking... And in fact, Nvidia and especially ATI are emphasizing overclockability more and more, which has become a strong sales argument. Software overclocking is very flexible to use (generally all you do is slide the frequency cursors and click "OK"), but it’s not free of drawbacks. It depends on a memory-resident program. That program consumes a small part of system resources, and can crash. The programs can contain bugs, or be incompatible with certain cards, certain driver versions or certain operating systems. What’s more, each time you re-boot the system you have to reconfigure everything.

Under the Hood

In short, a more permanent, more robust solution would be preferable – as with CPU overclocking, which won’t change unless you voluntarily modify the motherboard’s BIOS. And in fact, it works the same way with a graphics card. Permanent overclocking requires a change to the settings that are "hard-wired" in the card’s own BIOS. But while all you need to do to access your motherboard BIOS settings is press F1, F2 or Del when your PC is booting, the graphics card’s BIOS is not that easily accessible. You need a special utility to read and edit settings and save the new version, which will then be written to the card itself by flashing with yet another utility. Sound complicated? It may be, but it’s not at all impossible. And we’re here to tell you how to do it.

Keep Cool and Spend Your Money

However, if all this scares you, you can always go with a factory overclocked version, when the vendor does it for you. Models like this are extremely common, since third-party graphics cards manufacturers have found overclocking to be one way to set themselves apart from the competition. Certain ones, like XFX, may even owe all their success to the wide range of overclocked models they offer. But you should know that most of the time, pre-overclocked cards make you pay a lot for the few extra performance percentage points they offer.

Test configuration

Our tests were run on our reference system with an Asus P5E3 motherboard, an Intel QX6850 processor and 2 GB of Crucial DDR3. The operating system installed was the 32-bit version of Windows Vista SP1. For each card, we used the most recent versions of the drivers available at the time of the test – that is, ForceWare 174.53 and Catalyst 8.3.

Overclocking Nvidia: GeForce 9600 GT

But enough talk – let’s get down to brass tacks. We’re going to show you how to overclock your graphics card using two examples of recent cards – not that overclocking is only possible with new GPUs. It just seemed to make more sense to focus on today’s technology rather than yesterday’s.

Choose your weapons: GeForce 9600 GT and RivaTuner

We’ll start with a card from Nvidia, a GeForce 9600 GT. This card, which we tested at its recent launch, is based on a G94 GPU, a version of the G92 used in the GeForce 8800 GT and GTS V2 512 MB launched late in 2007. The G92 was itself a version of the G80 in the original GeForce 8800s that hit the market late in 2006. In other words, this is a processor with a well-known architecture and overclocking utilities that have been available long enough for us to become familiar with. The key utility for overclocking a GeForce is RivaTuner (downloadable here), an application that’s been around for some time and that gets its name from the Riva, the first GPU Nvidia produced a few years before the GeForce series. So, RivaTuner is perfectly mature and compatible with all Nvidia GPUs, and it’s updated very regularly. It’s a must-have.

Once you’ve downloaded, installed and launched the utility, click the little arrow to the right of “Customize,” in the second drop-down list entitled "Driver Settings." Select the icon that looks like a graphics card, "System settings."

The dialog that opens more or less speaks for itself. You can see three cursors – Core Clock, Shader Clock and Memory Clock.

Their function needs no explanation. But we should stop and take a closer look at the second one, for those of you who aren’t familiar with the architecture of Nvidia graphics processors. Since the GeForce 8, Nvidia GPUs have used two different clocks. One affects only the scalar ALUs (the famous stream processors) that form the unified shader units. The other affects the rest of the GPU. By default, these two frequencies are related by a ratio of approximately 2.5 (the ALUs run faster). This value isn’t universal to GeForce 8s, however, since the frequency increases by stages, as we’ll see later on.

With RivaTuner, you can increase the Core and Shader frequencies while keeping the 2.5 relation (you can also try changing that proportion). It’s not necessarily worthwhile, but it can give you a few extra MHz, since each portion of the GPU can have different frequency limits. In practice, though, you shouldn’t expect to gain all that much.

Trial and Error

Since each individual chip has its own capacities, there’s no way to know in advance what frequency you can push your GPU to and still maintain stable operation. So, overclocking has to be done gradually – by increments of 20 MHz, say. You start by increasing the speed of the GPU (and the shaders). At each level, quickly test the stability of the system by launching an application that makes a lot of 3D demands, such as a game. It goes without saying that the rest of your configuration has to be perfectly stable before you can judge the quality of the overclocking of your graphics card. Too much overclocking will cause the game to simply crash, or else cause artifacts of various types (such as groups of pixels of the same color, refresh faults, untrue colors, etc.)

Once you’ve found the limits of the GPU, it’s time to tweak the memory. You can increase memory in slightly larger frequency increments than for the GPU – for example 50 MHz. If at some point you start seeing artifacts, go back to the previous level and bump the frequency up by a smaller amount (say 20 MHz).

Take care, though, because the frequency you feed into RivaTuner won’t always be the one it actually applies to the graphics card. On certain processors, including all GeForce 8s, the evolution of the frequency is not linear; it moves in stages. So, in our case, setting the GPU (Core) to 725 MHz or 735 MHz works out to the same thing – an actual frequency of 729 MHz. On the other hand, a change that appears slight can in fact cross a threshold and bump up the frequency by some 10 MHz. This somewhat delicate operation is not a real problem, since RivaTuner can check the actual frequencies. For that, go to the "Hardware Monitoring" menu (see above).

Average gains

In our case, the G94 of our reference GeForce 9600 was pretty cooperative. Clocked at 650 MHz from the factory, it was able to be increased to 767 MHz and remain stable. This had the shaders running at 1920 MHz. We tried desynchronizing, but were only able to gain 30 MHz. We were able to increase the memory from 900 MHz to 1116 MHz. On the bottom line, that works out to a jump of 18% for the GPU and shaders and 24% for the memory. Not bad, but not excellent either. It was enough of a gain, however, to catch up with the performance of an 8800 GT, which is 15% faster than the 9600 GT in its factory state.