Munich - Anyone looking for fluid 3D gaming action or smooth video editing will need a powerful graphics card for their computer. When researching cards, potential buyers are typically faced with a range of manufacturer claims.

While these can be helpful, they are often only tangential to real quality and almost always require further explanation. One specification that does actually make a difference is the Graphics Processing Unit (GPU).

"That's the heart of a graphics card," explains Christian Wefers from hardware maker Asus. Far and away the most common chips found on graphics cards come from competitors Nvidia and ATI.

Their range of products is refreshed every few months as well. That means it's crucial to either do home research or talk to an expert at the store. A rough gauge of quality comes through the number of shaders - the more the better.

Modern graphic cards have their own proprietary RAM, just like the PC itself. GDDR3 is the current standard. Its predecessors, denoted with the "2" suffix, are significantly less powerful.

"The difference is substantial," says Michael Strohmeyer from Home of Hardware, a Bavaria-based Internet shop. He recommends at least 512 megabytes (MB) of RAM for current games - otherwise, jittery images can ruin the fun. More RAM is only required for extremely high resolutions, reports Christian Helmiss from Munich-based PC Welt magazine.

Processor speeds of 2 Gigahertz (Ghz) and more do speed up the cards, Christian Wefers says. The size of the memory controller is also important. That data provides insight into the data exchange rate between the graphics processor and the RAM. Anything below 256 bits threatens to turn into a bottleneck that causes jittery images, Helmiss claims.

DVI (Digital Visual Interface) is the most common interface type for connecting graphics cards with monitors. Older monitors still use the analogue VGA standard.

HDMI (High Definition Multimedia Interface) is required for resolutions above 1600 x 1200 pixels. PCIe (Peripheral Component Interconnect Express) is the current slot standard on PC mainboards for 3D graphics cards. Older AGP slots have now generally been phased out, Wefers notes.

The FLOPS (Floating Point Operations Per Second) count indicates how many calculations the graphic chip can make per second. Manufacturers like to tout that number. Yet because the practical application of that strength depends on the rest of the PC setup as well, the value should not be given much heed when selecting a product, Helmiss advises.

Another issue of only theoretical importance is the memory bus width, a gigabyte-based measurement of the data volume that a graphic cache can handle at once. In practice the value tends to vary from computer system to computer system, Helmiss says.

The DirectX software interface is important for the depiction of games. Each new version allows for new effects. Only Windows Vista users can work with the latest edition (Version 10); other operating systems are only able to work with DirectX 9, Helmiss explains.

Passionate computer gamers increase the graphics performance of their computers by using multi-GPU techniques to link several cards together. SLI (Scalable Link Interface) is Nvidia's version of the technique, while ATI calls it Crossfire.

As a high amount of computing effort is required to link the two cards, the setup does not provide exactly doubled performance, reports Christian Wefers from Asus.

Film lovers may be interested in graphics card with special video engines. That allows the graphics chip to take some of the decoding strain off the PCs main processor when converting film material into standard video formats. Nvidia calls the technology PureVideo, while ATI has dubbed it Unified Video Decoder (UVD).

Graphics chips are also trying to be less electricity hungry. Hybrid power technology, to date only available with Nvidia products, is one effort in that direction.

If the user switches to low-graphics office applications, then the motherboard uses its built-in graphics cards, simply switching off the power-hungry 3D card until it is needed. (dpa)