CPU overclocking is (relatively) simple and quite enjoyable. Plus it has an immediate and obvious benefit on your frame rates. There's a logical series of steps to follow with CPU overclocking, at the end of which you're more or less guaranteed a bump in performance.
By comparison, trying to overclock a graphics card is like trying to improve your chances of winning the London marathon by smacking the backs of your knees to make your legs work faster, while at the same time driving six-inch nails into your trainers for better grip.
In theory, it's a simple process. Both graphics card manufacturers Nvidia and AMD have opened up clock speed settings in their respective drivers, so all you have to do is move a slider to the right and you have faster graphics on a plate.
You can set the memory and GPU speeds separately, and all you need to remember is that if you increase the core clock slightly you'll need to accelerate the memory as well to ensure a smooth throughput of information. Simple? Not quite.
Faster speeds, however, also means more heat is generated, which means more errors introduced into computations. Graphics code tends to be quite robust, so these errors may not cause a game to crash, but they may well slow down rendering.
What's more, if the drivers suspect a problem has occurred, they may well revert the card to default speeds without telling you. This means that while many cards report back a successful overclock in the Windows driver, in our experience there's a very high chance that although they're running faster, performance will actually be worse.
The major issue is that any given graphics card is generally already performing close to its limit. The insane temperatures (up to 100°C) a GPU core operates at and the number of transistors on its surface means that only the strong survive even stock speed usage. Pushing them further is a recipe for disaster.
Don't expect to luck out with a tougher than normal card, either. Any chips which are discovered to have higher than average tolerances are picked for premium cards that arrive already overclocked. In turn, that means even those graphics cards have very little headroom for running at speeds faster than the manufacturers have already selected.
Be the GPU guru
The exceptions are graphics cards such as Asus' Republic of Gamers series, which not only open up more settings for overclocking in the drivers, but also have bespoke printed circuit boards (PCBs) for handling high speeds and extra cooling. Since they're so costly in the first place, though, they violate the first rule of overclocking, which is: Thou shalt not spend more than thou hast to.
So any graphics chip that can be overclocked has already been overclocked comprehensively and found its way into a high-end card with a bespoke cooler attached to it. Is there any point even finishing this article? Well, yes, actually.
Speeding up a graphics card is a hard task, but then again, so is making the perfect meringue or Beef Wellington. Yet these are worthy endeavours (especially the Beef Wellington). And since the limiting factor for most games is the graphics card the results can be impressive.
Like your processor, if you plan to get a decent amount of extra pace from a graphics card you are going to have to invest in a decent cooler. The bad news is that graphics coolers are generally quite fiddly and hard to fit.
To provide the amount of cooling you need in the space allocated, they've got to be quite a bit cleverer than the usual tower of metal with a fan and there are lots of screws to undo and springs to save.
Stay cool, honeybunny
Alternatively, you can buy water blocks to hook your graphics card into a liquid cooler, but in this case you must remember to provide some extra heat dissipation for the graphics memory too. Indeed, it's the GDDR5 chips which are more likely to start complaining as a result of being overclocked than the core itself.
Also like CPU overclocking, the key to quick, stable performance is to match extra megahertz with extra voltages. The trouble is that graphics drivers tend not let you do this easily.
The solution is to use the likes of MSI's Afterburner or RivaTuner to access these more esoteric settings.
Overclock your graphics card: Step by step
1. Pick a winner
Not all GPUs are equal in the overclocking world, and big, power-hungry chips are very hard to overclock to any degree that's worth it. We've had our best successes recently with AMD's Radeon HD5850, and even reference design boards can achieve impressive results.
2. Keeping it cool
The stock cooler on this particular card is pretty good, but if you turn up the fan speed it will get very noisy very quickly. For that reason, we're going to fit a Gelid Icy Vision unit (£40 from quietpc.com). The large fans cool everything on board much more efficiently and without sounding like a hurricane.
3. Getting started
First, you'll need to run an older benchmark such as 3DMark 05 or Far Cry 2 to get an idea of the base performance of your card. Any differences to your graphics performance due to an overclock will show up more starkly than if you use a demanding trial, such as the Unigine Heaven test.
4. Time for some tuning
Now open up the Catalyst driver panel and head to the Overdrive section. Unlock the padlock, and click 'Autotune'. Your GPU will now run through a batch of tests to find a speed it's happy running at. Once it's done that, run a few benchmarks to make sure it's stable. This is your starting point for overclocking.
5. Burn baby burn
Using MSI Afterburner, set the fan speed to around 50 per cent. We'll be able to dial this down for less noise later. Start overclocking with the memory settings. Set 3DMark or Unigine running on a loop in the background, and raise the GDDR speed by 10 to 20MHz a time until your machine crashes.
6. Mhz me, Mhz me
Set memory to its top speed and start work on the GPU itself. Increase the voltage first; we've increased it to 1,140mV for the HD4850 and then begin raising the GPU speed, just a few MHz until everything locks up. Once you've found a speed you're happy with, run the benchmark for an hour to check for stability.
First published in PC Plus Issue 299
Liked this? Then check out How to overclock your Intel CPU
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