View Full Version : GPU Overclocking

25th Feb 2013, 00:26
There have been some questions regarding GPU overclocking, and it was recommended that I make a thread to serve as a guide. This is that thread.

This thread serves only as a basic guide. I will not be covering hardware mods. I will not be telling you how to watercool your video card. What I will be telling you is how to do some basic overclocking using the stock cooler and a few simple tools. I'll cover terms, overclocking, stress testing, temperature monitoring, and troubleshooting.

You should read the entire guide before you follow any of the steps. Later steps may have information relevant to earlier steps.

Before we get started, there are a few basic things you'll need to download:
MSI Afterburner (http://event.msi.com/vga/afterburner/download.htm) (for overclocking and monitoring. Despite being MSI software, this will work on non-MSI cards just fine)
Unigine Heaven (http://unigine.com/products/heaven/download/) (for stress testing and verifying performance boosts)
Latest graphics drivers from AMD (http://www.amd.com) or NVIDIA (http://www.nvidia.com) (Radeon is AMD, Geforce is Nvidia)

There are a few terms you'll need to understand to make this easy.

Core Clock
This is the speed, in MHz, of the actual GPU core. Increasing this usually has the largest effect on performance, and is likely the first thing you'll run into a bottleneck on.

Memory Clock
This is the speed, in MHz, of the memory. Most video card memory runs at double-data-rate (DDR) or quad-data-rate (QDR). What this means is if you have a card that runs its memory at QDR and the memory says 1000MHz, it's effectively 4000MHz. This is important, as when you research safe values for your card, someone may say they're running their memory at one or the other, and it eliminates confusion as you'll understand why their number seems to be so much higher or lower than yours.

These three are used interchangeably, though I will be using the term VCore in this guide. This is the voltage the GPU core is operating at. Raising the VCore can help you get past overclocking barriers, but it has a caveat - increasing the voltage causes the card to consume more power, which in turn creates more heat. In addition, raising the voltage too high can significantly shorten the lifespan of your video card.

Power Limit
Some of the newer Geforce 6xx series cards and Radeon 7xxx series cards have a new setting called Power Limit. Power Limit allows you to adjust the TDP (Thermal Design Power) limit of the card. In simple terms, this means allowing the card to use more power without raising the VCore, allowing you to get a higher overclock. The big difference here is that VCore will always cause the card to consume more power, while Power Limit is simply a cutoff setting - you're telling the card it CAN consume more power, but it won't if it doesn't have to.

Step 1: Research
I can't stress this enough: spend a few minutes researching safe values for your GPU before you jump in. The basic settings we're going to be adjusting are core clock, memory clock, and core voltage (and for newer cards, power limit). Google is your friend here. Let's say you have a Radeon 5870. You might search for something along the lines of "radeon 5870 max safe vcore". Click around a few of the links and see what people are saying. I prefer to err on the side of safety, so if you end up with two numbers, say 1.3v and 1.2875v, I recommend staying at or below the lower recommended number.

You should also look up the standard idle and load temperatures for your card. Searching for reviews of your graphics card is a great way to do this, as they almost always contain temperature information. You'll want to watch the temperatures in Afterburner. If they vary significantly from what you find online, you may have a cooling issue.

Step 2: Setting up MSI Afterburner
I expect you can install Afterburner on your own - this concerns what to do once it's installed. When you launch Afterburner for the first time, you'll see something like this:

The graphs on the right will be different depending on your GPU configuration. In my case, I have two video cards, so it shows stats for GPU1 and GPU2.

The first thing you'll want to do here is click the Settings button at the bottom of the window. You'll be greeted with this screen:

If you have multiple GPUs, select the one you are overclocking from the Master Graphics Processor Selection drop-down box. Under Compatibility Properties, make sure your configuration matches what's shown in my picture - everything except Force Constant Voltage should be checked. The General Properties and Update Checking Properties sections are personal preference and you may set them as you wish. Once you have everything set, click OK to go back to the main Afterburner window.

Step 3: Test
We're going to do a quick stress test with the Unigine Heaven benchmark before we overclock. If for some reason your card is unable to complete the benchmark at stock settings, you absolutely do not want to push it harder by overclocking.

When you launch Heaven, you'll get a configuration screen. Set your preset to custom and use the following settings:

API: DirectX 11 (if DX11 is unavailable, use DirectX 9 instead)
Quality: High
Tessellation: Normal (unavailable in DirectX 9 mode)
Stereo 3D: DIsabled
Multi-monitor: Disabled
Anti-aliasing: 2x
Full Screen: Checked
Resolution: System

Why am I not suggesting that you set everything to high? We're trying to place as much stress as we can on the GPU without creating too many bottlenecks. If something causes too much of a bottleneck, it may cause other parts of the card to not be stressed as much.

Now, click the Run button, and once it's loaded, click the Benchmark button in the top left corner of the screen. The benchmark will take a few minutes to run, and at the end will give you an average framerate and a score. Write these down, as you can compare them with the numbers you get after overclocking.

If the test fails to finish (blue screen of death) or you see graphics corruption (trust me - you'll know if something is wrong), do not overclock. If anything, you might want to look at underclocking a bit. Under no normal circumstances should you the test fail or display graphics corruption at stock clock speeds.

Step 4: Overclocking GPU Core and Memory, and adjusting VCore (and power limit)
The first thing we're going to do is overclock your Core Clock and Memory Clock by a small amount. You'll need to have MSI Afterburner running, and be back on the main window:

Write down your default core and memory clocks. Then, grab a calculator and add 5% to them. Put the increased values into the boxes in Afterburner and hit Apply. Leave Afterburner open, and run the Heaven benchmark again.

NOTE: If you have a newer card and the power limit slider is adjustable (it will be stuck at 0 if your card doesn't support it), increase it as far as you can before continuing.

If Heaven is able to complete without issues, compare the new score it gives you to the original score. It should be a small bit higher - though we're kind of in margin of error range, so it may be very close. At this point, because we know the card is stable at these settings, you should click the Save button in Afterburner, and then select a Profile (1 is a good starting point). This will allow you to easily return to these values if need be. Note: Do not have Apply overclocking at system startup enabled. That should be left off until you've reached the maximum stable speed for your card - you don't want it to apply an unstable overclock the moment the computer starts up.

If the test fails, increase the VCore by a small amount. VCore is measured in millivolts (mV), and even a very tiny increase can make a fairly large difference. I recommend increasing vcore by 10-15 mV at a time. Make sure you have the default value recorded somewhere as well. Re-run the Heaven benchmark after each increase in VCore until it's stable. If it doesn't become stable after raising the VCore about 50mV or so (assuming that stays under the max safe value you researched earlier) with this small 5% overclock, you may just have a card that isn't going to run very much above stock speeds. This can happen, as no two cards overclock the same. It's entirely possible to get one that just doesn't want to overclock much at all.

Step 5: Tuning
Continue increasing the core and memory clocks by 5% of their original value. After each increase, run the Heaven benchmark again. During benchmarking, pay attention to the temperature that Heaven reports. Most modern cards will run in the 60s and 70s, perhaps even 80s. While you're technically okay at 90, I consider that too hot for daily use. I prefer not to go above the low 80s when the benchmark is running.

After each successful benchmark run, save your new values to your Afterburner profile. Continue the process of increasing the Core and Memory clocks until you get corruption and/or crashes (blue screens). When that happens, read the information on increasing VCore in the previous step. After a bit of VCore adjusting, you will likely be able to complete the benchmark again, at which point you should continue alternating between clock adjustments and VCore adjustments as necessary. You can also try adjusting just one of the clocks - core or memory - and not the other. They will almost never overclock by the same amount, so you may hit a wall on one before the other. When it comes to memory, however, keep reading as this is a special case on many cards.

At some point, you'll hit a wall. It could be that you're at the highest possible clocks for your card without exceeding a safe VCore level. It could be that your card just is not a good overclocker, and won't become stable at high overclocks even with VCore increases. It could be that your card is getting too hot (remember, 80s are a good place to stop). It could be that you're simply happy with your overclock. In any of these cases, you should have Afterburner set to your highest known stable overclock. When that's set, click the Settings button and make sure Start with Windows and Start Minimized are both enabled, and click OK. Then, at the very bottom of the main Afterburner window, make sure Apply overclocking at system startup is enabled.

Step 6: Memory Trickery and Troubleshooting
In the previous step, I mentioned that memory overclocking can be a little tricky. The cause of this is that some (but not all!) cards use error correcting memory. What that means is the memory will know when there's an error, and it will keep re-running the operation until things are correct. Now, imagine this: you've overclocked your memory by 20%, and increase it by another 5%. You rerun the benchmark, and your score is lower than the previous attempt. What's happening is the memory is overclocked too high, and is having to redo more than 5% (or whatever your last increase was) of its operations, resulting in lower performance. So, even when you've found your max stable overclock, you should try reducing your memory clock. If performance increases when you reduce the memory clock, you know it's running too high, and should continue decreasing it until performance starts decreasing again (at which point it's decreasing because there are no errors and you're just running the memory slower).

For troubleshooting, here are a few issues that people sometimes run into:

Unable to adjust VCore
Make sure Unlock Voltage Control is checked in Afterburner's settings. If you still can't adjust it, see if the manufacturer of your card has their own utility. Off the top of my head, EVGA has software called EVGA Precision, Sapphire has Trixx, and ASUS has GPU Tweak. Sometimes the manufacturer-specific utilities may allow you to adjust VCore when Afterburner won't. If you are still unable to adjust VCore, it may be that your card is simply voltage locked. There's no way around this without flashing a different bios or using hardware modifications, both of which are fantastic ways to void your warranty, and neither of which are covered in this guide.

Performance is lower when overclocking memory
See the beginning of Step 6.

Unstable at default settings
Your video card should never be unstable at stock clocks. Make sure you're running the latest drivers, and underclock if need be (follow the steps above, but decrease memory and core clocks instead of increasing). While this may be a sign of an unfixable (short of replacement) problem with your GPU, it's often a cooling issue. Even if your temperatures look fine, your card may have a hot spot due to poor thermal compound application. I won't cover those here, but you can google around for how to remove the cooler from your card and how to properly clean off the old/apply new thermal compound. This just happened to me with a Radeon 5770 about a week ago - it would crash within seconds of launching a demanding game or benchmark, even though temperatures were perfectly fine. I cleaned off the old thermal compound, applied new stuff, and it now works as well as the day I bought it.

Even at maximum safe VCore, I can't get more than a tiny overclock
Overclocking is not guaranteed. You may find that a lot of people get a 30% overclock on your particular card, but you can't get more than a 10% overclock no matter what you do. I hate to say it, but it's luck of the draw. Some hardware just won't overclock much.

Hopefully some of you find this information useful. I'm happy to answer any questions that anyone may have. If you find a problem or think there's information I left out that should be included, please let me know and I will edit this post ASAP.