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Graphics cards buying advice

How to buy a graphics card

Updating the graphics card in your PC is one of the most effective and cost-effective upgrades you can undertake. But with some graphics cards costing upwards of £300 you need to make sure you shell out for the correct device. Here's our graphics cards buying advice.

In the ever-moving graphics cards market, there’s always a new frontier to conquer. For today’s finest pixel-pumpers, DirectX 11.0 is the golden horizon. A constantly evolving programming interface developed by Microsoft, DirectX supplies programmers with effective ways to create games and other graphics applications.

Gamers moving up to a DirectX 11.0 graphics card will find advanced support for features including hardware tessellation, which creates smoother curves on surfaces, allowing for more lifelike results. DirectX 11.0 compute shaders are considerably more capable and flexible than existing shaders and add post-processing effects such as blurring to simulate movement. DirectX 11.0 has also been written to take greater advantage of multicore CPUs, evening out the strain high-end graphics processing places on the PC and resulting in smoother, more realistic-looking graphics.

See also: Group test - what's the best graphics card?

See also: Group test - what's the best budget graphics card?

Graphics cards buying advice: ATI versus nVidia

There are two names you need to know in graphics cards: ATI and nVidia. Much like the Intel and AMD duopoly in PC processors, these two manufacturers produce the chips around which others build graphics cards. It’s primarily the graphics chip that determines performance, but graphics card makers often make small tweaks to clock speeds or offer more powerful cooling systems and better software. If your chosen card brand isn’t available, you’ll get almost the same performance from a different vendor using the same graphics chip.

Graphics chip speed is usually denoted by a number, with a higher number describing a faster version of a card.

Graphics cards buying advice: Graphics memory and bandwidth

For smooth gameplay, you’ll want a card that’s supplied with at least 1GB of graphics memory (otherwise known as video RAM). For very high-end results, you may want to stretch to 1,536MB. Most decent graphics chips now come with GDDR5 RAM. This is more sophisticated than GDDR3 and will effectively quadruple the clock speed, whereas GDDR3 merely doubles it. You’ll therefore experience a huge leap in performance over your previous graphics card. Another important factor is the memory interface (or bus), which is determined by the chip. This governs how much data can be sent through at once. A 256bit interface can let through twice as much data as a 128bit interface. The memory can work at higher speeds, as determined by the clock speed. The cards with the best combination of memory interface size and clock speed should produce the best performance. A decent measure of this is the memory bandwidth, which is the memory interface divided by eight, multiplied by the effective memory clock speed. If the memory is GDDR5, you get the effective speed by quadrupling the basic memory clock; for GDDR3 you double it. Measured in gigabytes per second (GBps), the higher the memory bandwidth, the better the card will be able to handle textures and other features.

Graphics cards buying advice: Switchable shaders

Stream processors are a significant feature of today’s cards, able to work as either vertex or pixel shaders. Older graphics chips used dedicated vertex shaders and pixel shaders, but if a game used more of one than the other, the card wasn’t used to its full potential. When an object has been ‘created’ by the shaders, a texture or image will be applied to it. Texture units work with the shaders to apply textures as quickly as possible. This is a resource-intensive process, so the more texture units, the better the fill rate will be. We calculate the fill rate by multiplying the number of texture units with the core clock speed of the card. The higher the resulting number of texels (texture elements), the more textures the card can fetch. Raster output units (ROPs) are also important since these turn the information from vertex and pixel shaders to complete pixels to create the final image.

Graphics cards buying advice: Practical and price considerations

When buying a graphics card, always check you’ve got enough room in your case fo it. Also ensure you have enough spare power connectors from the power supply unit (PSU). The cheapest cards require no additional power, but most cards require one six-pin connector and some will need two. The PSU should be rated high enough to handle the demands of the graphics card.

Every card now has a digital video port. Most have DVI and/or Display Ports, and the best cards also offer HDMI. If you plan to use ATI’s EyeFinity, which stretches your display over multiple monitors, you’ll need to ensure your card has enough ports and connectors.

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