Factors that affect graphics card performance - what makes a good graphics card?

GPU type

Arguably, the most important factor is the type of GPU (graphics processing unit) used by the card. The internal workings of each GPU are very different and there are massive differences between the performance given by different GPU families, even when running at the same clock speeds.

Hardware Direct X support

Direct X is like the middle man between the game and the card, designed so that programmers don't have to write different code specifically for each graphics card. Recently Microsoft has brought out Direct X 9, which includes new instructions over 8.1. Many games are now being released that make use of DX9 and a graphics card with hardware support for this will run these games significantly better than the last generation of DX8.1 capable cards. You should be able to run DX9 games on a DX8.1 graphics card, but performance will suffer.

Graphics Memory

A graphics card needs to hold a lot of textures and other information in memory and it needs very fast access to this data. This is why graphics cards have their own onboard RAM. Bandwidth and speed are the most important factors affecting video ram, and this is generally more important than the speed of the GPU, or the quantity of ram. The speed of the RAM on a graphics card will differ between manufacturers, which is why it is always worth finding out and comparing ram speeds. The Sparkle 5600 and the Terratec 5600 Pro in this roundup are a good example of how speed matters more than quantity. The Sparkle has 128meg of ram at 500 mhz, and the otherwise identical Terratec has 256meg of ram at 400mhz. The Sparkle card performs slightly better.

GPU Speed

The clock rate of the GPU itself is of course a factor in graphics performance. ATI's new XT range for example, are just the same cards as the non XT models, but with a slightly higher clock rate GPU, giving a significant performance boost. The GPU speed of a card does not tend to vary between manufacturers like the RAM speed can.

Overclocking

Overclocking your graphics card will not turn your aging Geforce 2 into an FX5900, but it is a good way of extending the life of an old card a little, or to squeeze every last drop of performance out of a new card.

Your card may come with some overclocking tools, or you might need to download some. Powerstrip is the most popular utility for this.

Some card manufacturers, such as Gainward, offer pre-overclocked cards guaranteed to run at higher speeds. If you want the extra speed and don't mind paying a little more, then this can be worth it.

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