Graphics-card technology moves at a rapid pace, and it can be difficult for all but the most tech-savvy to keep up. In the January 07 issue of PC Advisor, we've tested a selection of the best cards around. But if the daunting jargon and obscure terminology of PC graphics technology leaves you cold, our essential guide to buying a graphics card is here to help.

This article appears in the January 07 issue of PC Advisor, onsale now in all good newsagents.

Computers don't stay young forever. As we all know, they often require a spot of tinkering under the hood to keep up with newer machines. Normally it's a memory or storage modification that calls for the screwdriver set, but graphics-card upgrades are popular too – particularly among gamers keen to play the latest titles.

Yet a new graphics card offers much more than superior gaming performance. It can vastly improve your PC's ability to display and play videos, with many cards now including a Vivo (video in, video out) feature.

Although there are loads of brands to choose from, almost every card is powered by an ATI or nVidia GPU (graphics processing unit) and at least 256MB of RAM. Prices start at around £60 for the no-frills variety and escalate to over £400, more than you'd shell out on an entire dedicated games console.

For everyday tasks, any current-generation card will do, but 3D polygon pushing is where the men are separated from the boys. There are few more stressful tasks for a PC than running a modern game.

The processor, RAM and entire graphics sub-system are busy reproducing and responding to the frenetic action on screen.

Gaming nirvana starts at the magic 60fps (frames per second) mark, but frame rates twice that are becoming a reality, thanks to modern graphics cards. They can also enable the use of higher resolutions and assorted eye candy. The full detailed results of our exhaustive graphics card tests are included on the Jan 07 cover disc. For general advice, read on.

Getting the right balance

Slotting an exotic graphics card into a middle-aged PC has its consequences - and we don't just mean the hefty credit card bill. When choosing a new card keep your PC's specifications as balanced as possible in order to avoid bottlenecks.

If you've installed a powerful graphics card you'll need to couple it with a swift processor to get the full benefit. If you don't, the processor will bottleneck, typified by a game's performance remaining the same at lower resolutions. You could simply increase the workload by increasing the screen resolution. This will alleviate the strain on the processor, but go too far and the graphics card's processor will struggle. Don't overlook the demands on the PSU (power supply unit), either. Some graphics cards need to draw up to 130W from your PC's power supply, so check yours is up to the job. If not, you could suffer an unstable system afflicted by lockups, erratic 3D performance and unplanned reboots.

Even with high-end cards boasting up to 1GB RAM onboard, there is still a requirement for healthy levels of system RAM – especially if you crank up the resolution.

It's all in the detail

Cranking up certain visual effects will cut your frame rates, although this will be less of a concern for high-end cards. The most common speed killers are antialiasing and anisotropic filtering, but detailed shadows, reflections and higher dynamic range can all take their toll.

AA (antialiasing) is a technique used to smooth jagged edges on screen; these are generally most noticeable on curved or diagonal lines. The traditional solution is to raise the resolution. These days, AA offers a more sophisticated method, but it comes at a price: reduced speed.

It's for this reason that most games – and even the settings in Control Panel – allow varying levels and types of AA. This way there's more chance of hitting the right balance between graphical quality and frame rates. Anisotropic filtering governs the way mapped textures appear and the amount of clarity they maintain, even at a distance. Much like AA, AF takes its toll on the frame rate and should be treated with respect when using low-end cards. But for clean-looking, detailed textures, AF greatly contributes to overall image quality.

Most games now use shadows and reflections to increase graphical realism, but it can take considerable chunks out of frame rates. Fear's soft shadows option, for example, has a noticeable slowing effect. If you're struggling for speed, start by switching off this option.

HDR (Higher Dynamic Range) is a more recent drain on frame rates. This allows the reproduction of a greater tonal range, giving games a more realistic appearance – especially when reproducing extremes of light and dark. ATI and nVidia both support this feature, but ATI offers better support for games to run both HDR and AA at the same time.

The very latest cards have more built-in memory than their predecessors. The average for budget models is 256MB, while 512MB or even 1GB is the norm for more exotic hardware. More memory allows higher-resolution textures to be used, but the speed of the RAM is also vital for ensuring smooth gameplay.

How much RAM is too much?

Cheaper cards generally use DDR (double data rate) or DDR2 memory, usually running at speeds from 400MHz to 800MHz. Pricier models use the quicker DDR3 or, more recently, DDR4, with speeds reaching a staggering 2GHz. Faster RAM increases the memory bandwidth, allowing information to be loaded and offloaded more quickly. For this reason, we don't recommend spending too much on a 512MB budget card – the real-world performance benefits will be negligible compared with a 256MB variant.

As well as reduced memory bandwidth, cheaper cards will have a narrower architecture with fewer pixel pipelines. This results in a reduction in the amount of information that can be processed by the GPU at any one time.

Video on a PC

Aside from powering increasingly demanding games, a capable graphics card can ensure you get fantastic playback on a PC.

ATI's Avivo (advanced video in, video out) software enables video encoding for output to various devices, including iPods and Sony's PSP (PlayStation Portable). nVidia uses PureVideo, which – when combined with the relevant hardware – provides enhanced features such as advanced de-interlacing and H.264 support for new HD (high-definition) optical standards such as Blu-ray Disc and HD-DVD.

Many mid- and high-end cards sport a Vivo connection for connecting older analogue devices, such as a camcorder or VCR. This facility allows video to be recorded on to a PC or output to a TV. Some cards, such as ATI's series of All-In-Wonders, go a step further and sport radio and TV aerial connections.

Future physics

Graphics cards will eventually provide real-time physics calculations for future generations of games. ATI and nVidia are quick to claim their cards are ideally suited for the task. Their dual-card configurations not only power the onscreen action, but are capable of managing the clever physics behind the scenes.

SLI and Crossfire

Cutting-edge graphics technology crams more than 380 million transistors into the small silicon square that is a GPU. But for games enthusiasts running heady resolutions on mammoth screens, even high-end cards can struggle with some of the more demanding titles.

Enter ATI Crossfire and nVidia SLI (scalable link interface). By running two graphics cards in tandem, it's possible to double the graphical power of a PC. Obviously you'll need a compatible board with the two required PCI Express slots, not to mention a robust power supply. The performance can be staggering – as can the cost. For high-end configurations it may even exceed £800.