As most readers probably know, nVidia and ATI are the one-ton gorillas of the videocard market. These two perennial powerhouses have been jousting back and forth for top spot in the graphics market for years now. ATI currently holds the overall performance crown, but nVidia has a stranglehold on the lucrative mid-range market with its 6600GT GPU as of the writing of this guide.

Since there's a 95% chance that any recent computer uses a video card from one of these two companies, this article deals primarily with overclocking those products. While the primary purpose and effect of overclocking ATI or nVidia videocards is the same, the software and even the procedures used can differ, so each company's cards are covered in a separate section.

The most recent video cards from either company tend to be highly overclockable, though historically nVidia has held an advantage in this regard. Some previous-generation cards from ATI have a form of overclocking 'lock' implemented on them, causing the core and memory clock speeds to return to stock as soon as a 3D application or game is started. More on this later in the article.

Updating Videocard Drivers

The first thing to do before overclocking a videocard is to acquire the most recent driver set for it. NVidia's ForceWare and ATIs Catalyst driver sets are universal, meaning they cover all recent videocards made by their respective companies. All that needs to be done is to visit the website of the card's manufacturer and download the latest version of the drivers, then install them. Note that at the time of this guide, the latest version of the RivaTuner utility used for overclocking in this article did not fully function with the latest version of the ATI Catalyst driver suite (5.5), though it still worked for overclocking purposes. Readers may want to stick with the Catalyst 5.4 drivers for full functionality until an update is released.

Benchmarking and Overclocking

This article assumes that readers are already familiar with (or at least are aware of the existence of) the common 3D performance benchmarking programs like 3DMark05.

To get the best out of an ATI or nVidia videocard in terms of overclocking, a consistently repeatable 3D benchmark like FutureMark's 3DMark 2001SE or 3DMark05 is needed to test the new settings each time core or memory speeds change.

Since most modern videocards run at slower speeds when rendering a 2D image such as the Windows desktop, the fact that a card can render the desktop correctly when overclocked is not a real test of its stability. To truly test an overclocked card's stability, a full-screen 3D benchmark needs to be run completely and without error.

Download 3DMark 2001SE or 3Dmark 2005. For an nVidia 5xxx or 6xxx series card, or a Radeon 9xxx or Xxxx series card, use 3DMark05; otherwise, use 3DMark 2001SE.

Install 3DMark and run the (non-overclocked) system through a round of the benchmark with everything at its default setting. Record the final score. This is the baseline for comparing the video card's performance before and after overclocking.