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.

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