AMD may not have the current performance crown, but there's no doubt its processors still represent unbelievably good value.

And with its list of high-end overclocking features the Black Edition more than makes up for any performance shortfall with sheer fun and flexibility.

Retailing at around £130 the quad-core Phenom II X4 955 is one of the best quad-core options on the market, and the fact it comes with multiplier and voltage unlocked is the icing on the cake.

But just how flexible is the Phenom 955 at overclocking and how do you get the best out of it? We're going to look at the options available and how you can get the best out of an overclock.

Keeping things accessible we'll only be using air-cooled solutions, as anything else would deserve a feature on its own. The tools of the overclocker remain the same: a good cooler, a good motherboard and a good selection of settings to play with.

We're making use of the solid Titan Fenrir NK85TZ cooler, it is a perfect example of a higher-end air cooler. Thankfully to back this up we have the mighty Asus Crosshair IV Formula motherboard to play with. This arms us with a top-notch mobo with every overclocking setting you could possibly want.

The usual suspects

That only leaves one part left: the actual overclocking. To help track our performance increases we'll be using the tried and tested standard tools, the results of which can be found scattered around the pages of PC Format much like freebie USB flash drives are scattered around the office.

For processor testing we have Far Cry 2, World in Conflict, x264 encoding, WinRAR benchmark and Cinebench R11.5. This varied collection of benchmarks will help us get an idea of how our overclocking efforts have succeeded in improving performance for a number of real-world situations. We'll also note the core temperatures as well, as our mums like that.

When you get stuck into overclocking, the staple ways of pushing up the speed of a processor are to increase the system bus, increase the processor's clock multiplier – if you're lucky enough to own the right processor – or do a bit of both. While these techniques have stayed the same, the way you go about it have changed.

In the bad-old days you'd fiddle with motherboard jumpers and BIOS settings remain a core technique, but now Windows based utilities offer as much flexibility.

Volting her up

The other stalwart of overclocking is the CPU voltage setting, as you increase the processor speed to maintain stability it's necessary to increase the voltage supplied to the processor as power demands increase.

This isn't a blunt instrument, increasing the voltage too much can cause as much instability as increasing the bus speeds. It has to be balanced with speed increases. Increased voltage also leads to greatly increased core temperatures, as we'll see. As a reference, the core temperature under load running at the stock speed was 38.5°C.

The first important step is to reduce the memory bus speed to the lowest speed setting, ideally 400MHz (800MHz double-data rate) with RAS/ CAS of 8-8-8-8-24. These will, as much as possible, help eliminate memory-based errors from any lockups. That way you can be more certain a lockup is caused by the processor throwing a wobbly.

The safe approach is to start by increasing processor speed around 10MHz at a time, but this would take quite some time. We prefer jumping in with both feet and assuming a free 10 per cent increase is a safe bet, so with the 3.2GHz Phenom II 955 that's an initial overclock to 3.5GHz or a FSB speed of 219GHz.

We use the X264 HD benchmark as the base stability test for our efforts, increasing the FSB 1MHz at a time – that's a 16MHz processor increase – using the AMD OverDrive software utility. Eventually we hit 3,728MHz with the FSB at 233MHz before X264 fell over, though Windows itself remained stable.

We cranked the FSB back down and running the other benchmarks we eventually settle on 228MHz and 3,648MHz as being stable. The core temperature is up a little at 40.5°C.

The whole point of the Black Edition is that it comes multiplier unlocked. This enables you to increase processor speed without knocking the system bus off its stock speed, which is better for everyone. After our initial 'old-school' approach we switch to increasing speed through multiplier steps.

She canna take it

We returned to the unstable level of 3,700MHz using a 200MHz FSB and a multiplier of 18.5x and increased the voltage by a single step – usually around 0.0125v – from the stock 1.350v until the system is stable again. It's then a return to slowly increasing the processor speed via the FSB until it becomes unstable again.

This happy electron-base ballet took us up to a maximum of 3,904MHz with a 1.56 core voltage, 205MHz FSB, a 19x multiplier and a scarily elevated core temperature of 60.5°C! This unsurprisingly wasn't particularly stable, crashing under load with our best solid results being 3,838MHz with the 19x multiplier and a 202MHz FSB.

1. In the rigging

Step 1

A good quality motherboard and a good pair of memory sticks are the foundations of easy overclocking. Without access to the right setting you'll find travelling close to the speed of light an easier way of increasing processor speeds than trying to fiddle about under the hood yourself.

2. Windy Miller

Step 2

A heavy duty air-cooler not only offers improved cooling but quieter running over stock coolers. One with a heavy-duty heatpiped copper base and 120mm fan is going to provide more efficient cooling that the standard block type. You can overclock on the stock cooler of course, just not as much.

3. Slap and tickle

Step 3

Remember, a good application of thermal paste is going to help your cooling efforts, this means don't just slap it on but equally don't omit it. We find applying an initial tiny amount, spreading this around with heatsink itself, then removing and cleaning the majority off just the cooler offers the best results.

4. Blue BIOS

Step 4

For years the traditional way to overclock has been to use the BIOS and that remains the same today. The best overclocking boards will provide a dedicated section to adjust the settings for the memory, processor and system bus along with automatic settings, preset options and recovery.

5. AMD Overdrive

Step 5

On the whole we've opted to use the AMD Overdrive software utility, it provides easy access to the settings we need and offers very good monitoring features. It offers a basic mode that provides basic overclocking and the Advanced mode that offer access to all the processor controls you could want.

6. Third party

Step 6

Most motherboard manufacturers will also provide their own overclocking utilities. This Asus one offers a decent automatic mode, though such utilities tend to err on the side of safety a little too much. In this case it limits itself to a maximum core voltage of 1.4, so its maximum speed is a paltry 3,450MHz or so.

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First published in PC Format Issue 244

Liked this? Then check out How to overclock DDR3 RAM

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