How to build your own desktop: Processor and Motherboard

Time to upgrade your system? Brush up on your PC-building skills with our three-part guide.

In Part 1 of our three-part series, we take a look at the ins-and-outs of motherboards and CPUs, including buying tips and installation advice.

Introduction: Why build a PC?

Building your own PC can save you money, and it allows you to create a system that’s perfectly suited to your needs.
It’s also a great way to gain familiarity with the way the various parts of your system work together – and it’s very easy to do.
That’s because every component and connector in a modern PC is strictly standardised, so you can safely buy off-the-shelf components and assemble them at home to make a working system. It isn’t for absolute beginners, however, but if you’re the sort of person who’s happy opening up your PC’s case to upgrade the RAM or fit a new graphics card, there’s nothing to fear.

Building your own PC might not always be cheaper than buying a complete package. It’s a very competitive industry, and the professionals work to tight margins on complete systems.

But there’s plenty of scope to save money by reusing parts you may already own, such as the case, power supply and hard disk from an older PC. You may even be able to keep your operating system without paying for a new licence.
In this feature, we’ll show you how to choose parts that work together, and what you can reuse to assemble a fully functioning, well-balanced system.

Choosing your parts and building your PC

Building a PC isn’t hard, but you must take care when deciding exactly which parts you’re going to use. Naturally, you need to choose parts that are compatible with one another: the key caveat to building your own PC is that you’ll be taking responsibility for this yourself, rather than relying on the experience of a system builder.

A good approach is to start by deciding on the components that are most important to you, then choosing other parts to suit. For example, if you start by deciding you want an Intel Core i5 processor, this will narrow down the range of motherboards you can choose from – which in turn may affect the case you choose.
Conversely, if having a small case is your chief priority, this will restrict the motherboards available to you, which could force your hand when it comes to other components.
In this three-part feature, we’ll walk you through the process of specifying and assembling a desktop PC. (We won’t cover peripherals such as the keyboard and monitor, which simply plug in to your PC.)
If you pick unusual parts, it’s possible you might run into particular questions that call for a little internet research. But if you’re building a typical PC using common components you’ll find everything you need right here.

Processor and Motherboard

When you’re building a new system, you’ll almost invariably need to buy a new processor and motherboard. It’s unlikely you’ll be able to slot a new chip into your existing board: Intel has updated its processor sockets and chipsets several times over the past few years, so a modern processor won’t work with last year’s motherboard.

AMD has kept things a bit more stable, sticking with the Socket AM3 architecture for its Athlon and Phenom CPUs since 2009 – but its very latest range of Fusion A-Series processors uses a brand-new socket, dubbed Socket FM1.
There’s a huge range of processors and boards to choose from, depending on your priorities. Different CPU models perform differently, while some can be overclocked and some include built-in graphics.
Not all motherboards support all of these features, and different boards offer different expansion options, which may include USB 3 sockets and SATA 6Gbits/sec ports.
There are plenty of other options: see our regular reviews and check out the A-List for worthy alternatives.
Potential pitfalls

It ought to go without saying, but make sure the board you choose has the right socket for your CPU. A Socket 1156 board won’t work with a Socket 1155 processor, and so forth. Pay attention to the board’s form factor – its size and shape – too.
If you want to use a standard case and power supply, any ATX-compliant motherboard will do, but if you want a smaller midi-tower, look for the micro-ATX form factor. You can fit a micro-ATX board into an ATX case, but not vice versa. Less common motherboard sizes such as BTX and mini-ITX need cases to match their specific formats.
How to install it
Mounting the CPU onto the board is straightforward. For an AMD chip, lift the arm next to the socket and gently drop in the processor, so that its pins fall all the way into the holes (use the printed arrow in the corner to make sure the chip is the right way round). Once in place, lower the arm and clip it into place to secure the chip.

Intel chips use a slightly different system: here, when you lift the lever, a metal casing will open to reveal the socket.
Intel processors don’t have protruding pins, so just place the processor gently into the socket, using the arrow in the corner and notches at the sides to ensure it’s aligned. Lower the lever to lock the casing and secure the chip.

Cooler and thermal paste

When you buy a CPU as a “retail” package, it comes with a standard heatsink and fan unit. If you buy an “OEM” or “tray” model, you’ll need to find one. Most AMD processors use a standard cooler attachment, so you may be able to reuse an older cooler. This isn’t the case with Intel: here, a new CPU will probably need a new cooler.
You can buy third-party coolers, too. These are typically quieter than stock models and they keep temperatures lower, which can help with overclocking. Some cooling systems use water to conduct heat from the CPU, but that’s for hard-core enthusiasts only.
Potential pitfalls
Make sure that the power cable for your fan is long enough to reach the power connector on the motherboard. If it isn’t, try fitting the cooler the other way round. It’s also worth double-checking that your cooler is fitted properly before you power on the PC for the first time: if your CPU overheats then your computer will crash.
How to install it
Check whether the bottom of the heatsink has been pre-treated with thermal paste. If not, apply some paste manually – small tubes can be bought cheaply from most component suppliers. Make sure the top of your CPU and the bottom of the cooler are clean, then spread a thin, even layer of paste onto the top of the processor.

 Next, mount the cooler. For an AMD cooler you do this by fitting the two metal flaps over the plastic tabs on the motherboard and engaging the lever to secure it.
To fit a standard Intel cooler, first check that the four fasteners around the cooler have been turned clockwise as far as they’ll go (away from the direction of the arrow).
Then align the cooler with the holes in your motherboard and press down each fastener until it clicks into place. If you need to remove the cooler, turn the fasteners anti-clockwise and pull them up. Some specialist coolers use screws instead of these standard fasteners: these attach to a plate that goes on the underside of the motherboard.
Once your cooler is in place, you’ll need to plug it into the motherboard to power the fan. There will normally be a four-pin connector labelled FAN near to the processor socket for this purpose.