The first thing to consider when buying a desktop PC is what you'll be using it for. The systems that top our PC charts tend to offer good all-round specifications, but they may not be ideal if your interest lies particularly in playing games or you intend to keep it on display in the living room. As ever, our PC reviews are intended only as a guide, and you may do better by contacting the vendor to customise your PC's specification.

For the kids' homework: If all you need is a basic machine on which your children can research homework topics and write the odd essay, you'll be throwing your money away on a top-end PC. Don't pay out for a fast processor, gaming graphics, a full-HD monitor or a Blu-ray drive – you don't need any of it. The bundled software is likely to be of greater importance than the hardware here, particularly if your children are using Microsoft Office at school, for instance. And if the kids push you for a laptop, remember this: not only do desktops offer a better performance-pound ratio, they also keep the little munchkins in one place where you can keep an eye on them.

For work: As with the above scenario, there's no need to pay out for a top-of-the-range system unless your work involves intensive video and image editing. If you regularly work with spreadsheets, get a large monitor or consider adding a second. And if you're on the road a lot for business, consider whether a laptop might be more useful. Alternatively, if yours is the kind of work where there just aren't enough hours in the day to get things done, consider a fast processor, plenty of RAM, and a solid-state disk for faster bootups and system responsiveness

For gaming: Hardcore gamers will want a top-end graphics card and a fast processor, and these don't come cheap. PC vendors offer a range of futuristic system cases specifically designed for gamers, with transparent side panels, LED-illuminated internals and more. You'll also want a large flat-panel display with a response rate of 8ms or less. With a lot of powerful components under the hood, you'll need a case that keeps noise and heat to a minimum.

See also: games reviews

For editing images and video: If you aren't already under Apple's Mac OS X spell, a good screen, a quad-core processor, a decent graphics card and plenty of RAM are the important features here.

See also: Photo Advisor

For tinkering: If you want a PC you can upgrade to your heart's content, look for a roomy system case with spare drive bays and fan-mounting points, and a motherboard with plenty of free slots. You'll also need a 750W-plus-rated power supply unit. Intel's Sandy Bridge processors demand a new type of motherboard, so buying into this technology now will future-proof your PC. Look for USB 3.0 and SATA 6Gbps support if you want to add the latest high-speed storage. Ensure you're running a 64bit operating system, too.

See also: Upgrade Advisor

For playing videos, music and photo slideshows: If you intend to use your desktop in the living room, make sure it's a quiet one with plenty of internal noise dampening. Alternatively, consider a more compact media-centre PC that can be hooked up to your TV, or an all-in-one PC that will look great in the corner with no unsightly system case or cables. Storage capacity is important here, as is the ease of backing up files – you may wish to get a machine with more than one hard drive. A Blu-ray drive and a large full-HD monitor will also be sought-after specifications.

See also: Digital Home Advisor

PC buyers' guide: Processor and motherboard

Intel's second generation of Core-series processors (aka 'Sandy Bridge') wipes the floor with all other chips in performance terms. Each processor includes an updated version of Intel's integrated graphics solution, providing accelerated graphics encoding and VGA and HDMI outputs. This means non-gamers can potentially save some cash by omitting a discrete graphics card, and will still be able to watch full-HD (1920x1080-pixel) video.

Although we test all our review systems at their standard settings, several members of the Sandy Bridge processor family have been specifically designed for overclocking, denoted by a 'K' at the end of their product name. These chips are slightly more expensive than their non-K variants but are multiplier-unlocked, allowing for easy overclocking in the Bios. They demand a P67-chipset-based motherboard, however, which won't support the processor's integrated graphics. Also note that if you do wish to overclock your CPU, the standard processor cooler fitted by Intel may need to be upgraded, and you'll require at least a 750W-rated power supply unit (PSU).

For non-K Sandy Bridge processors, an H67-chipset-based motherboard is a cheaper alternative. These motherboards are not compatible with first-generation Core-series chips, so buying into the technology now will future-proof your PC.

The fastest processor in the new series is the 3.4GHz Core-i7-2600K. At 3.3GHz, the Core i5-2500K offers a slightly lower specification. It has no support for hyperthreading and 6MB rather than 8MB of level 3 cache. Both chips are also available in cheaper non-K versions that don’t offer the same overclocking potential.

Turbo Boost technology allows a processor to overclock a single core (or all four when used with a 'K' processor and a P67 motherboard) when the system is under load.

The more cores a processor has, the more able it is to multitask and run intensive multithreaded applications such as video editing. All the chips in the Sandy Bridge family are quad-core, as are the older Core i5-700-, -800- and -900-series CPUs. Of the older chips, dual-core processors such as the i5-600 series tend to have higher clock speeds, and thus will perform better when working with single-threaded applications. Single-core processors will be noticeably slower.

For budget desktop PCs, good value can still be had by older Intel Core-series CPUs, such as the Core i7-950 and -870, and Core i5-760. AMD also offers quad-core processors, but none can currently keep up with Intel’s latest offerings.

NEXT PAGE: memory, storage and display >>

PC buyers' guide: Memory

If a fast processor speeds up your PC, a large bank of memory stops it from slowing down. Don't buy a Windows 7 PC with less than 2GB of system RAM. Most are fitted with at least 4GB, although we've seen £1,000-plus systems offering as much as 16GB. Sandy Bridge PCs should come with at least 8GB. For the PC to access more than 4GB of memory, and for systems running dual-graphics setups, you'll also need to be running a 64bit operating system.

Sandy Bridge processors and the Core i5-700- and 800-series chips require DDR3 RAM, while older chips can use less expensive DDR2. The triple-channel architecture of the Core i7-900-series processors requires you to install memory chips in threes (3GB or 6GB, for example), but Core i7-800- and -2000-series CPUs use a two-channel system. DDR3 memory is getting cheaper and bodes well for performance. 

If you plan to upgrade the memory later, check how many slots are free on the motherboard. If, for example, a PC vendor has installed four 1GB sticks of RAM, thus occupying all four of the motherboard's memory slots, an upgrade will be more expensive than if it had installed two 2GB sticks - in our example you would need to replace your existing memory rather than add to it.

PC buyers' guide: Storage

Falling prices mean that even a budget PC should be able to include a one-terabyte (1TB) hard drive; more expensive systems may provide twice this capacity. A 1TB drive should be adequate for most users, but you can never have too much storage space: digital photos, video and music will quickly fill a reasonably sized drive.

Backing up your files to an portable hard drives or network storage is essential: 1TB is a lot of information to lose in one go if your drive should fail. Alternatively, consider mirroring a pair of internal drives, although noise levels will increase.

Adding a second hard drive is one of the simplest upgrades you can undertake. If you wish to do so internally, check the system case has a spare drive bay available. Some system cases offer a top-mounted SATA port for fast docking of a hard drive, while external drives can quickly and easily be added via USB. 

For compatibility with the latest high-speed storage, check that the motherboard offers support for USB 3.0 and SATA 6 gigabits per second (Gbps).

In systems costing more than £1,000, a supplementary solid-state disk (SSD) is a must - with a minimum capacity of 60GB if you're running Windows 7.

Flash-based storage provides a noticeable boost to bootup times and system responsiveness. Solid-state drives remain expensive for now, but prices are starting to come down.

PC buyers' guide: Optical drives

Laptop and netbook manufacturers often omit an optical drive to increase portability. For a desktop PC there's no excuse. That said, don't base your purchasing decision on the DVD drive - it's a cheap upgrade.

Get a drive that can write to the DVD+/-R formats at 16-speed or better. If you want to get 8.5GB on to one disc, get a drive that can write to dual-layer discs at eight-speed (DVD+R DL).

Blu-ray drives are too expensive to be found in budget PCs, but where they are specified you'll also want a large full-HD (1920x1080-pixel) screen and a set of external speakers to complete the multimedia experience. PC vendors often offer DVD/Blu-ray combo drives; expect DVD speeds to be slower here.

PC buyers' guide: Display

The display is often overlooked by PC vendors wanting to curtail costs. However, it's the component you'll spend most of your time looking at, and is even more important if you do a lot of photo or video editing. Quality varies hugely among screens, and it's not only the size and resolution you need to consider. Also investigate viewing angles, whether the screen offers height, tilt and pivot adjustments, the pixel pitch, the response rate (8ms or below will minimise blur on fast-moving action), brightness and contrast. Where possible, it's a good idea to see the screen in person before you buy.

Most desktop PCs now come with full-HD (1920x1080-pixel) flat-panel displays, although the less you pay for your PC the smaller the screen tends to be. Aim for a 21.5in model with a budget PC, and around 25in with a system costing more than £1,000. Be advised that manufacturers often round up their figures for advertising purposes - a 21.5in screen becomes 22in, and a 23.6in screen becomes 24in, for example.

A 25in full-HD screen will not only provide a better experience when watching videos, playing games and working with spreadsheets than a 21.5in model, but it will also render text and icons slightly larger.

If you want to hook up a games console or projector, look for a screen with dual analogue and digital inputs. VGA is an analogue connection, while DVI, HDMI and DisplayPort are three types of digital connection.

Models with LED backlighting aren’t necessarily better, but can offer improved contrast, lower power consumption and a thinner, more desirable design.

NEXT PAGE: graphics card, PSU and audio >>

PC buyers' guide: Graphics card

With the best graphics cards retailing for more than £300, a budget PC is unlikely to suit a hardcore gamer. However, decent graphics cards get cheaper all the time, and budget PCs can now handle games that were unthinkable a few months ago. 

If you have no interest in playing games, Intel’s Core i3 and i5 CPUs come with integrated graphics processors that deliver around double the performance of older Intel integrated solutions. Sandy Bridge chips are even faster and offer features such as dual-monitor outputs. These machines support HD video and Windows’ Aero effects without the need for a separate graphics card. 

AMD’s ATI Radeon HD 5450 is a popular choice for a budget machine. It doesn’t offer a great speed advantage over Intel GMA integrated graphics, but it adds support for DirectX 11.0. If you really want to play games, nVidia’s GeForce GT 240 will provide some extra speed. Be prepared to lower your graphics settings to achieve smooth gameplay, however.

If gaming is important to you and you're prepared to spend a little more on your PC, look for an ATI Radeon HD 6870 or Geforce GTX 460. In a gamer-friendly system costing £1,000-plus, aim for an ATI Radeon HD 6970 or nVidia GeForce GTX 580.

nVidia cards offer support for realistic object interactions in games supporting PhysX and are able to display 3D content. Recent ATI cards can also be connected to multiple displays. Look out for pre-overclocked graphics cards, as well as those that come with custom cooling solutions. 

Many nVidia and ATI graphics cards can be upgraded to dual-card setups later. To take advantage of this, your motherboard and power supply must be compatible. However, the current crop of motherboards which support the new Sandy Bridge processors have only limited support for multiple graphics cards, so buy the fastest single card you can afford. A single-card setup leaves more space for sound cards or TV tuners.

PC buyers' guide: Power supply unit

With no power-hungry components installed, a budget PC needs only a basic PSU. A 450W or 500W model is a good starting point. 

For all other systems, the level of power you require will depend on the graphics card you want to use. Look for at least a 500W unit or 750W-plus if you plan to add another card or overclock the CPU. 

Get a model with a full set of SATA and PCI Express connectors to make later upgrades easier. 

PC buyers' guide: Sound

Most desktop PCs come with onboard sound rather than a separate sound cards, and budget machines tend to rely on the tinny speakers built into the monitor for playback. However, if you're buying a system with a large screen and a Blu-ray drive, you'll also want a decent set of external speakers. For the best playback, get a set that includes a subwoofer.