Choosing your parts and building your PC

A 400W PSU will provide more than enough juice for a regular desktop system. You only need a more powerful supply if you’re using at least one top-of-the-range graphics card. It’s best to afford yourself some headroom, though: a power supply that’s running close to its capacity will run hotter and less efficiently.

Modular power supplies let you disconnect the cables you’re not using so that they don’t clutter the inside of your case. Whether that’s worthwhile or not depends on how often you plan to rummage inside the PC.

Potential pitfalls

If you’re a tinkerer, it’s worth investing in a case that affords easy access. If you plan to drive your PC hard, you might want a case with built-in fans to keep things cool. Or, you can buy third-party fans and add them to most cases yourself. In some cases, the positioning of the power supply can make it difficult to mount hard disks and optical drives later on – if you think this might be a problem, skip ahead to the relevant sections and install your drives before continuing.

How to install it

If your power supply is separate from the case, slot it into the cavity at the top rear of the case and secure it from behind with screws.

Next, it’s time to install your motherboard into the case and plug the various case and PSU connectors into it. If your case is cramped, you may want to plug in these connectors before putting the board into place.

The procedure for installing the board depends on your particular case design. With most tower-type cases you’ll want to lie the case on its right-hand side (as viewed from the front), take off the left-hand side and lower in the board so that its USB ports and other connectors line up with the hole at the rear.

PC Build 4 Case 640x480

You may need to screw in metal spacers to set the board at the correct height – these should be included with the case. Make sure they line up with the screwholes in the motherboard.

The board will also come with a backplate cover that you can press into the rear of the case to keep things neat and reduce dust. Once everything is in place, secure the board with plenty of screws.

Now it’s time to connect the power. The large 24-pin connector from the power supply connects to the wide power socket on the motherboard. The plug will fit only the right way round. Four pins at the end of this connector may be separated from the other 20, but you can press the whole plug in as one.

The CPU has its own power connector as well: you’ll find the socket on the motherboard next to the processor itself. There are two standards for this connector; four-pin and eight-pin. The connectors are cross-compatible, however, so you can happily plug a four-pin CPU plug into one side of an eight-pin socket. It works the other way round, too: you can plug an eight-pin plug into a four-pin socket and leave the spare pins hanging off the end.

Finally, hook up the case connectors – little plugs on spindly coloured wires – to the motherboard, to support things such as the power button, hard disk LED, and front USB and audio ports. Ordinarily, these slide onto bare pins sticking up from the motherboard. Check the manual to find the right place to attach them.


All of Intel’s current desktop processors have built-in graphics, as do AMD’s latest Fusion processors. Older AMD processors have no graphics, but they can be used with motherboards that feature an integrated GPU. So if you’re assembling a PC for desktop use, you may not need a graphics card at all.

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