At the heart of every good gaming system is a good graphics card.
This 3D powerhouse generates the images you see on the screen. In basic terms a 3D game holds the information required to generate a 3D world and it's the graphics card that takes this information and turns it into an on-screen image.
Two companies make the only gaming cards worth considering: the AMD Radeon and Nvidia GeForce cards. Currently AMD has its HD5000 range and Nvidia its GTX 200 and 400 ranges.
The short rule is the more you spend the higher the resolution, the more effects you can use and importantly, the smoother the latest games will play. Read our graphics card reviews to see which cards offer the type of performance you need.
Generally you'll want at least an AMD Radeon 57xx or better, and from Nvidia at least a GTS250 or better yet a GTX460 model.
To complicated the situation both AMD and Nvidia offer systems that enable you to connect more than one of their own cards together. AMD calls it CrossfireX and Nvidia called it SLI. Your motherboard has to support this feature and provide enough PCIe slots to add more than one card. But it's a useful way to improve performance either straight away if you buy two, three or four cards, or at a later date by adding in a second.
To work efficiently graphics cards require their own special memory that comes built-in. Lower-end cards will provide around 256MB to 512MB of memory, higher-end cards start with 768MB moving up to 1,024MB and higher. This memory enables the card to store high-detailed models and textures, helping make the 3D world look even more realistic.
Cards with less memory have to make do with less detailed models and textures. It sounds too simple but with a gaming PC it pays to spend as much as you can on the graphics card. It's important not to skimp on the processor but a good graphics card is the cornerstone for any decent gaming system.
Our article 15 best graphics cards in the world today is a great shortlist of cards for gaming PCs.
Motherboards for gaming PCs
A gaming PC doesn't have to be a high-end system every time but generally it's going to be running the latest processor technology and therefore it'll need an up-to-date motherboard.
For AMD processors this is the AM3 socket technology with DDR3 memory. On the Intel platform this is socket 1156 for its Core i3 and i5 processors or the higher-end socket 1366 for Core i7, both again running DDR3 memory.
You will still see plenty of AMD AM2(+) and Intel Socket 775 motherboards on offer and if you're after a more modest gaming PC, these will suffice though with a weaker selection of dual-core processors such as the AMD Athlon X2 and the Intel Core 2 range.
Unlike the home PC and media centre PC systems that can make do with onboard 'integrated' graphics, a gaming PC has to use a dedicated plug-in graphics card to get any decent level of 3D performance.
These are added using a PCIe slot, confusingly these come in various speeds with x16 being the fastest, along with x8, x4 and x1. The x16 slot is important as this is also a size requirement for PCIe graphics cards. Confusingly an x16 sized slot can run at x8 or other speeds but that's fine, as long as it's physically an x16 size then you can plug-in a graphics card!
All motherboards will offer at least one x16 slot. If you're planning on running an AMD CrossfireX or Nvidia SLI multi-graphics card set-up then the motherboard will require two or more x16-sized slots and be certified suitable for CrossfireX, SLI or both.
Besides the graphics all motherboards will provide suitable six- or eight-channel surround sound that will enhance your gaming experience. Alongside a suitable number of internal SATA hard drive connections and external USB ports.
To choose a new motherboard, take a look at our motherboard reviews.
Processors for gaming PCs
As we've covered you'll be looking at one of the latest AMD or Intel sockets and therefore processors. Either a strong dual-core or multi-core processor should be on your shopping list. AMD offers a number of affordable triple-core and quad-core Athlon II X3/X4 processors, but ideally look to its Phenom II X4 range which is a strong but affordable quad-core offering.
From Intel its new Core i3 socket 1156 processors tend to best the AMD Athlon II X3/X4 processors, whilst being a little more expensive. Its Core i5 socket 1156 processors are delivering very fast performances matching the best AMD Phenom II X4 models.
If you can afford it the high-end Core i7 socket 1366 processor is unmatched, but there is a large price premium for effectively a small boost in speed. But there's a wide selection of good gaming processors on offer ranging from £50 all the way up to £500.
Our processor reviews will help you choose the right processor for your money.
Memory for gaming PCs
A good gaming PC will need a reasonable amount of memory. We've already covered that it's likely the processor and motherboard will be DDR3. The price of DDR3 has fallen enough that it's comparable to DDR2 and it does offer a speed advantage, especially on the Intel Core i3/5/7 platforms.
Ideally 4GB is a base level for a gaming PC and this will be made up from two sticks of 2GB DDR3 memory, so you gain the benefits of dual-channel memory. If you're lucky enough to afford a Core i7 system with triple-channel memory, you'll want three 2GB DDR3 sticks of memory to make up a total of 6GB.
The issue this raises is you'll need a 64-bit installation of Windows. Until now most installations were 32-bit and only allowed access to around 3.2GB of memory, any more installed would be ignored. A 64-bit installation can take full advantage of 4GB and more. If you're buying Windows 7 it comes with both a 32-bit and 64-bit install disc.
Check out our memory reviews for a selection of RAM for your PC.
Gaming PC monitors
To get a thrilling gaming experience a big-screen with a high-resolution is the order of the day. Old-style CRT displays aren't available any more and it's lovely flatscreen LCDs all the way.
Resolution should be your key concern: there's no point spending hundreds of pounds of an amazing graphics card, just to buy a monitor that can only display 1280x720 pixels.
At the high-end 27- to 30-inch monitors can hit 2560x1600 resolutions and this is the maximum currently available but these displays tend to top the £1,000 mark. More affordably there's a wide selection of 24-inch monitors that provide a good 1920x1080 resolution that can start as low as £140.
The step below this are the 20- and 22-inch models, however you tend to find they're not significantly cheaper and the drop in resolution and screen size doesn't really offset the savings.
Beside size and resolution response rate and contrast ratio are important for clarity of moving images and colour reproduction, but stated figures can be somewhat misleading and the subject is something of a gray area, so read our monitor reviews to get a better idea.
Our monitor reviews feature plenty of choice for your games machine.
Cases, cooling and power
With the need for housing large PCIe graphics cards your average gaming PC tends to be a little on the large side. The other consideration is that all those heat-producing, power-hungry graphics cards and processors good cooling is the order of the day.
So it's wise to take some time picking a large, attractive case that comes with plenty of ventilation and pre-installed with case fans. Besides this is a cooler for your processor, a higher-end model will generate less noise as it'll cool it more efficiently, so be less distracting.
A suitable power supply unit will also be on your shopping list. For gaming one that's at least 700 watts and comes with enough PCIe connectors to power your graphics cards, if you're planning on using more than one, it what you need to shop for. Some cases do come with these but they will tend to be cheaper units that you will simply have to replace.
To help you further, we've rounded up the best coolers and fans for gaming PCs.
Liked this? Then check out 15 best graphics cards in the world today
Sign up for TechRadar's free Weird Week in Tech newsletter
Get the oddest tech stories of the week, plus the most popular news and reviews delivered straight to your inbox. Sign up at http://www.techradar.com/register